Systems and methods for deriving a motion vector prediction in video coding

ABSTRACT

A method for determining a reference index for a reference picture list is disclosed. A reference picture list structure in one of a sequence parameter set and a slice header is decoded. A reference index for the reference picture list structure is derived according to a value of a reference picture list flag. A number of reference index active syntax in the slice header is decoded, if a number of entries in the reference picture list structure is greater than 1. The number of reference index active syntax is defined for i. A variable is derived by adding one to a value of the number of reference index active syntax. A value subtracted one from a value of the variable specifies a maximum reference index for the reference picture list.

TECHNICAL FIELD

This disclosure relates to video coding and more particularly totechniques for signaling reference pictures for coded video.

BACKGROUND ART

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, laptop or desktop computers,tablet computers, digital recording devices, digital media players,video gaming devices, cellular telephones, including so-calledsmartphones, medical imaging devices, and the like. Digital video may becoded according to a video coding standard. Video coding standards mayincorporate video compression techniques. Examples of video codingstandards include ISO/IEC MPEG4 Visual and ITU-T H.264 (also known asISO/IEC MPEG-4 AVC) and High-Efficiency Video Coding (HEVC). HEVC isdescribed in High Efficiency Video Coding (HEVC), Rec. ITU-T H.265,December 2016, which is incorporated by reference, and referred toherein as ITU-T H.265. Extensions and improvements for ITU-T H.265 arecurrently being considered for the development of next generation videocoding standards. For example, the ITU-T Video Coding Experts Group(VCEG) and ISO/IEC (Moving Picture Experts Group (MPEG) (collectivelyreferred to as the Joint Video Exploration Team (JVET)) are studying thepotential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard. The Joint Exploration Model 7 (JEM 7), AlgorithmDescription of Joint Exploration Test Model 7 (JEM 7), ISO/IECJTC1/SC29/WG11 Document: JVET-G1001, July 2017, Torino, IT, which isincorporated by reference herein, describes the coding features undercoordinated test model study by the JVET as potentially enhancing videocoding technology beyond the capabilities of ITU-T H.265. It should benoted that the coding features of JEM 7 are implemented in JEM referencesoftware. As used herein, the term JEM may collectively refer toalgorithms included in JEM 7 and implementations of JEM referencesoftware. Further, in response to a “Joint Call for Proposals on VideoCompression with Capabilities beyond HEVC,” jointly issued by VCEG andMPEG, multiple descriptions of video coding were proposed by variousgroups at the 10th Meeting of ISO/IEC JTC1/SC29/WG11 16-20 Apr. 2018,San Diego, Calif. As a result of the multiple descriptions of videocoding, a draft text of a video coding specification is described in“Versatile Video Coding (Draft 1),” 10th Meeting of ISO/IECJTC1/SC29/WG11 16-20 Apr. 2018, San Diego, Calif., documentJVET-J1001-v2, which is incorporated by reference herein, and referredto as JVET-J1001. “Versatile Video Coding (Draft 2),” 11th Meeting ofISO/IEC JTC1/SC29/WG11 10-18 Jul. 2018, Ljubljana, SI, documentJVET-K1001-v5, which is incorporated by reference herein, and referredto as JVET-K1001, is an update to JVET-J1001.

Video compression techniques reduce data requirements for storing andtransmitting video data by exploiting the inherent redundancies in avideo sequence. Video compression techniques may sub-divide a videosequence into successively smaller portions (i.e., groups of frameswithin a video sequence, a frame within a group of frames, slices withina frame, coding tree units (e.g., macroblocks) within a slice, codingblocks within a coding tree unit, etc.). Intra prediction codingtechniques (e.g., intra-picture (spatial)) and inter predictiontechniques (i.e., inter-picture (temporal)) may be used to generatedifference values between a unit of video data to be coded and areference unit of video data. The difference values may be referred toas residual data. Residual data may be coded as quantized transformcoefficients. Syntax elements may relate residual data and a referencecoding unit (e.g., intra-prediction mode indices, motion vectors, andblock vectors). Residual data and syntax elements may be entropy coded.Entropy encoded residual data and syntax elements may be included in acompliant bitstream. Compliant bitstreams and associated metadata may beformatted according to data structures.

SUMMARY OF INVENTION

In one example, a method for determining a reference index for areference picture list, the method comprising: decoding a referencepicture list structure in one of a sequence parameter set and a sliceheader; deriving a reference index for the reference picture liststructure according to a value of a reference picture list flag;decoding a number of reference index active syntax in the slice header,if a number of entries in the reference picture list structure isgreater than 1, wherein the number of reference index active syntax isdefined for i; and deriving a variable by adding one to a value of thenumber of reference index active syntax, wherein a value subtracted onefrom a value of the variable specifies a maximum reference index for thereference picture list.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example of a system that maybe configured to encode and decode video data according to one or moretechniques of this disclosure.

FIG. 2 is a conceptual diagram illustrating coded video data andcorresponding data structures according to one or more techniques ofthis disclosure.

FIG. 3 is a conceptual diagram illustrating a data structureencapsulating coded video data and corresponding metadata according toone or more techniques of this disclosure.

FIG. 4 is a conceptual drawing illustrating an example of componentsthat may be included in an implementation of a system that may beconfigured to encode and decode video data according to one or moretechniques of this disclosure.

FIG. 5 is a block diagram illustrating an example of a video encoderthat may be configured to encode video data according to one or moretechniques of this disclosure.

FIG. 6 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure.

FIG. 7 is a flow chart illustrating an example of a method fordetermining reference picture list information for a reference picturelist according to one or more techniques of this disclosure.

DESCRIPTION OF EMBODIMENTS

In general, this disclosure describes various techniques for codingvideo data. In particular, this disclosure describes techniques forsignaling reference pictures for coded video. Signaling of referencepictures according to the techniques described herein may beparticularly useful for improving video distribution system performanceby lowering transmission bandwidth. It should be noted that althoughtechniques of this disclosure are described with respect to ITU-T H.264,ITU-T H.265, JVET-J1001, and JVET-K1001 the techniques of thisdisclosure are generally applicable to video coding. For example, thecoding techniques described herein may be incorporated into video codingsystems, (including video coding systems based on future video codingstandards) including block structures, intra prediction techniques,inter prediction techniques, transform techniques, filtering techniques,and/or entropy coding techniques other than those included in ITU-TH.265. Thus, reference to ITU-T H.264, ITU-T H.265, JVET-J1001, andJVET-K1001 is for descriptive purposes and should not be construed tolimit the scope of the techniques described herein. Further, it shouldbe noted that incorporation by reference of documents herein should notbe construed to limit or create ambiguity with respect to terms usedherein. For example, in the case where an incorporated referenceprovides a different definition of a term than another incorporatedreference and/or as the term is used herein, the term should beinterpreted in a manner that broadly includes each respective definitionand/or in a manner that includes each of the particular definitions inthe alternative.

In one example, a method of signaling reference picture list comprisessignaling one or more candidate reference picture lists in a parameterset, and signaling an index to one of the candidate reference picturelists in a header associated with a region of a picture.

In one example, a device comprises one or more processors configured tosignal one or more candidate reference picture lists in a parameter set,and signal an index to one of the candidate reference picture lists in aheader associated with a region of a picture.

In one example, a non-transitory computer-readable storage mediumcomprises instructions stored thereon that, when executed, cause one ormore processors of a device to signal one or more candidate referencepicture lists in a parameter set, and signal an index to one of thecandidate reference picture lists in a header associated with a regionof a picture.

In one example, an apparatus comprises means for signaling one or morecandidate reference picture lists in a parameter set, and means forsignaling an index to one of the candidate reference picture lists in aheader associated with a region of a picture.

In one example, a method of decoding video data comprises parsing one ormore syntax elements included in a parameter set, the syntax elementsindicating one or more candidate reference picture lists, parsing anindex from a header associated with a region of a picture, the indexindicating one of the candidate reference picture lists, and generatingvideo data based on the indicated candidate reference picture list.

In one example, a device comprises one or more processors configured toparse one or more syntax elements included in a parameter set, thesyntax elements indicating one or more candidate reference picturelists, parse an index from a header associated with a region of apicture, the index indicating one of the candidate reference picturelists, and generate video data based on the indicated candidatereference picture list.

In one example, a non-transitory computer-readable storage mediumcomprises instructions stored thereon that, when executed, cause one ormore processors of a device to parse one or more syntax elementsincluded in a parameter set, the syntax elements indicating one or morecandidate reference picture lists, parse an index from a headerassociated with a region of a picture, the index indicating one of thecandidate reference picture lists, and generate video data based on theindicated candidate reference picture list.

In one example, an apparatus comprises means for parsing one or moresyntax elements included in a parameter set, the syntax elementsindicating one or more candidate reference picture lists, means forparsing an index from a header associated with a region of a picture,the index indicating one of the candidate reference picture lists, andmeans for generating video data based on the indicated candidatereference picture list.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

Video content typically includes video sequences comprised of a seriesof frames. A series of frames may also be referred to as a group ofpictures (GOP). Each video frame or picture may include a one or moreslices, where a slice includes a plurality of video blocks. A videoblock includes an array of pixel values (also referred to as samples)that may be predictively coded. Video blocks may be ordered according toa scan pattern (e.g., a raster scan). A video encoder performspredictive encoding on video blocks and sub-divisions thereof. ITU-TH.264 specifies a macroblock including 16×16 luma samples. ITU-T H.265specifies an analogous Coding Tree Unit (CTU) structure (which may bereferred to as a Largest Coding Unit (LCU)) where a picture may be splitinto CTUs of equal size and each CTU may include Coding Tree Blocks(CTB) having 16×16, 32×32, or 64×64 luma samples. As used herein, theterm video block may generally refer to an area of a picture or may morespecifically refer to the largest array of pixel values that may bepredictively coded, sub-divisions thereof, and/or correspondingstructures. Further, according to ITU-T H.265, each video frame orpicture may be partitioned to include one or more tiles, where a tile isa sequence of coding tree units corresponding to a rectangular area of apicture.

In ITU-T H.265, a CTU is composed of respective CTBs for each componentof video data (e.g., luma (Y) and chroma (Cb and Cr)). Further, in ITU-TH.265, a CTU may be partitioned according to a quadtree (QT)partitioning structure, which results in the CTBs of the CTU beingpartitioned into Coding Blocks (CB). That is, in ITU-T H.265, a CTU maybe partitioned into quadtree leaf nodes. According to ITU-T H.265, oneluma CB together with two corresponding chroma CBs and associated syntaxelements are referred to as a coding unit (CU). In ITU-T H.265, aminimum allowed size of a CB may be signaled. In ITU-T H.265, thesmallest minimum allowed size of a luma CB is 8×8 luma samples. In ITU-TH.265, the decision to code a picture area using intra prediction orinter prediction is made at the CU level.

In ITU-T H.265, a CU is associated with a prediction unit (PU) structurehaving its root at the CU. In ITU-T H.265, PU structures allow luma andchroma CBs to be split for purposes of generating correspondingreference samples. That is, in ITU-T H.265, luma and chroma CBs may besplit into respect luma and chroma prediction blocks (PBs), where a PBincludes a block of sample values for which the same prediction isapplied. In ITU-T H.265, a CB may be partitioned into 1, 2, or 4 PBs.ITU-T H.265 supports PB sizes from 64×64 samples down to 4×4 samples. InITU-T H.265, square PBs are supported for intra prediction, where a CBmay form the PB or the CB may be split into four square PBs (i.e., intraprediction PB sizes type include M×M or M/2×M/2, where M is the heightand width of the square CB). In ITU-T H.265, in addition to the squarePBs, rectangular PBs are supported for inter prediction, where a CB mayby halved vertically or horizontally to form PBs (i.e., inter predictionPB types include M×M, M/2×M/2, M/2×M, or M×M/2). Further, it should benoted that in ITU-T H.265, for inter prediction, four asymmetric PBpartitions are supported, where the CB is partitioned into two PBs atone quarter of the height (at the top or the bottom) or width (at theleft or the right) of the CB (i.e., asymmetric partitions include M/4×Mleft, M/4×M right, M×M/4 top, and M×M/4 bottom). Intra prediction data(e.g., intra prediction mode syntax elements) or inter prediction data(e.g., motion data syntax elements) corresponding to a PB is used toproduce reference and/or predicted sample values for the PB.

JEM specifies a CTU having a maximum size of 256×256 luma samples. JEMspecifies a quadtree plus binary tree (QTBT) block structure. In JEM,the QTBT structure enables quadtree leaf nodes to be further partitionedby a binary tree (BT) structure. That is, in JEM, the binary treestructure enables quadtree leaf nodes to be recursively dividedvertically or horizontally. Thus, the binary tree structure in JEMenables square and rectangular leaf nodes, where each leaf node includesa CB. As illustrated in FIG. 2 , a picture included in a GOP may includeslices, where each slice includes a sequence of CTUs and each CTU may bepartitioned according to a QTBT structure. In JEM, CBs are used forprediction without any further partitioning. That is, in JEM, a CB maybe a block of sample values on which the same prediction is applied.Thus, a JEM QTBT leaf node may be analogous a PB in ITU-T H.265.

Intra prediction data (e.g., intra prediction mode syntax elements) orinter prediction data (e.g., motion data syntax elements) may associatePUs with corresponding reference samples. Residual data may includerespective arrays of difference values corresponding to each componentof video data (e.g., luma (Y) and chroma (Cb and Cr)). Residual data maybe in the pixel domain. A transform, such as, a discrete cosinetransform (DCT), a discrete sine transform (DST), an integer transform,a wavelet transform, or a conceptually similar transform, may be appliedto pixel difference values to generate transform coefficients. It shouldbe noted that in ITU-T H.265, CUs may be further sub-divided intoTransform Units (TUs). That is, an array of pixel difference values maybe sub-divided for purposes of generating transform coefficients (e.g.,four 8×8 transforms may be applied to a 16×16 array of residual valuescorresponding to a 16×16 luma CB), such sub-divisions may be referred toas Transform Blocks (TBs). Transform coefficients may be quantizedaccording to a quantization parameter (QP). Quantized transformcoefficients (which may be referred to as level values) may be entropycoded according to an entropy encoding technique (e.g., content adaptivevariable length coding (CAVLC), context adaptive binary arithmeticcoding (CABAC), probability interval partitioning entropy coding (PIPE),etc.). Further, syntax elements, such as, a syntax element indicating aprediction mode, may also be entropy coded. Entropy encoded quantizedtransform coefficients and corresponding entropy encoded syntax elementsmay form a compliant bitstream that can be used to reproduce video data.A binarization process may be performed on syntax elements as part of anentropy coding process. Binarization refers to the process of convertinga syntax value into a series of one or more bits. These bits may bereferred to as “bins.”

As described above, intra prediction data or inter prediction data isused to produce reference sample values for a block of sample values.The difference between sample values included in a current PB, oranother type of picture area structure, and associated reference samples(e.g., those generated using a prediction) may be referred to asresidual data. As described above, intra prediction data or interprediction data may associate an area of a picture (e.g., a PB or a CB)with corresponding reference samples. For intra prediction coding, anintra prediction mode may specify the location of reference sampleswithin a picture. In ITU-T H.265, defined possible intra predictionmodes include a planar (i.e., surface fitting) prediction mode(predMode: 0), a DC (i.e., flat overall averaging) prediction mode(predMode: 1), and 33 angular prediction modes (predMode: 2-34). In JEM,defined possible intra-prediction modes include a planar prediction mode(predMode: 0), a DC prediction mode (predMode: 1), and 65 angularprediction modes (predMode: 2-66). It should be noted that planar and DCprediction modes may be referred to as non-directional prediction modesand that angular prediction modes may be referred to as directionalprediction modes. It should be noted that the techniques describedherein may be generally applicable regardless of the number of definedpossible prediction modes.

For inter prediction coding, a motion vector (MV) identifies referencesamples in a previously coded picture (i.e., picture available whendecoding or encoding a current picture) for coding a current video blockin a current picture and thereby exploits temporal redundancy in video.For example, a current video block may be predicted from referenceblock(s) located in previously coded picture(s) and a motion vector maybe used to indicate the location of the reference block. A motion vectorand associated data may describe, for example, a horizontal component ofthe motion vector, a vertical component of the motion vector, aresolution for the motion vector (e.g., one-quarter pixel precision,one-half pixel precision, one-pixel precision, two-pixel precision,four-pixel precision), a prediction direction and/or a reference pictureindex value. Further, a coding standard, such as, for example ITU-TH.265, may support motion vector prediction. Motion vector predictionenables a motion vector to be specified using motion vectors ofneighboring blocks. Examples of motion vector prediction includeadvanced motion vector prediction (AMVP), temporal motion vectorprediction (TMVP), so-called “merge” mode, and “skip” and “direct”motion inference. Further, JEM supports advanced temporal motion vectorprediction (ATMVP), Spatial-temporal motion vector prediction (STMVP),Pattern matched motion vector derivation (PMMVD) mode, which is aspecial merge mode based on Frame-Rate Up Conversion (FRUC) techniques,and affine transform motion compensation prediction.

Residual data may include respective arrays of difference valuescorresponding to each component of video data. Residual data may be inthe pixel domain. A transform, such as, a discrete cosine transform(DCT), a discrete sine transform (DST), an integer transform, a wavelettransform, or a conceptually similar transform, may be applied to anarray of difference values to generate transform coefficients. In ITU-TH.265, a CU is associated with a transform unit (TU) structure havingits root at the CU level. That is, in ITU-T H.265, as described above,an array of difference values may be sub-divided for purposes ofgenerating transform coefficients (e.g., four 8×8 transforms may beapplied to a 16×16 array of residual values). It should be noted that inITU-T H.265, TBs are not necessarily aligned with PBs.

It should be noted that in JEM, residual values corresponding to a CBare used to generate transform coefficients without furtherpartitioning. That is, in JEM a QTBT leaf node may be analogous to botha PB and a TB in ITU-T H.265. It should be noted that in JEM, a coretransform and a subsequent secondary transforms may be applied (in thevideo encoder) to generate transform coefficients. For a video decoder,the order of transforms is reversed. Further, in JEM, whether asecondary transform is applied to generate transform coefficients may bedependent on a prediction mode.

A quantization process may be performed on transform coefficients.Quantization approximates transform coefficients by amplitudesrestricted to a set of specified values. Quantization may be used inorder to vary the amount of data required to represent a group oftransform coefficients. Quantization may be realized through division oftransform coefficients by a scaling factor and any associated roundingfunctions (e.g., rounding to the nearest integer). Quantized transformcoefficients may be referred to as coefficient level values. Inversequantization (or “dequantization”) may include multiplication ofcoefficient level values by the scaling factor. It should be noted thatas used herein the term quantization process in some instances may referto division by a scaling factor to generate level values ormultiplication by a scaling factor to recover transform coefficients insome instances. That is, a quantization process may refer toquantization in some cases and inverse quantization in some cases.

With respect to the equations used herein, the following arithmeticoperators may be used:

-   -     Addition    -   − Subtraction    -   * Multiplication, including matrix multiplication    -   x^(y) Exponentiation. Specifies x to the power of y. In other        contexts, such notation is used for superscripting not intended        for interpretation as exponentiation.    -   / Integer division with truncation of the result toward zero.        For example, 7/4 and −7/−4 are truncated to 1 and −7/4 and 7/−4        are truncated to −1.    -   ÷ Used to denote division in mathematical equations where no        truncation or rounding is intended.

$\frac{x}{y}$

Used to denote division in mathematical equations where no truncation orrounding is intended.

Further, the following mathematical functions may be used:

-   -   Log2(x) the base-2 logarithm of x;

${{Min}\left( {x,y} \right)} = \left\{ {\begin{matrix}{x;} & {x<=y} \\{y;} & {x > y}\end{matrix};{{{Max}\left( {x,y} \right)} = \left\{ \begin{matrix}{x;} & {x>=y} \\{y;} & {x < y}\end{matrix} \right.}} \right.$

-   -   Ceil(x) the smallest integer greater than or equal to x.

With respect to the example syntax used herein, the followingdefinitions of logical operators may be applied:

-   -   x && y Boolean logical “and” of x and y    -   x∥y Boolean logical “or” of x and y    -   ! Boolean logical “not”    -   x?y:z If x is TRUE or not equal to 0, evaluates to the value of        y; otherwise, evaluates to the value of z.

Further, the following relational operators may be applied:

-   -   < Greater than    -   >= Greater than or equal to    -   > Less than    -   <= Less than or equal to    -   == Equal to    -   != Not equal to

Further, it should be noted that in the syntax descriptors used herein,the following descriptors may be applied:

-   -   b(8): byte having any pattern of bit string (8 bits). The        parsing process for this descriptor is specified by the return        value of the function read_bits(8).    -   f(n): fixed-pattern bit string using n bits written (from left        to right) with the left bit first. The parsing process for this        descriptor is specified by the return value of the function        read_bits(n).    -   u(n): unsigned integer using n bits.    -   ue(v): unsigned integer 0-th order Exp-Golomb-coded syntax        element with the left bit first.

As described above, according to ITU-T H.265, each video frame orpicture may be partitioned to include one or more slices and furtherpartitioned to include one or more tiles. FIG. 2 is a conceptual diagramillustrating an example of a group of pictures including slices. In theexample illustrated in FIG. 2 , Pic₃ is illustrated as including twoslices (i.e., Slice₁ and Slice₂) where each slice includes a sequence ofCTUs (e.g., in raster scan order). It should be noted that a slice is asequence of one or more slice segments starting with an independentslice segment and containing all subsequent dependent slice segments (ifany) that precede the next independent slice segment (if any) within thesame access unit. A slice segment, like a slice, is a sequence of codingtree units. In the examples described herein, in some cases the termsslice and slice segment may be used interchangeably to indicate asequence of coding tree units. It should be noted that in ITU-T H.265, atile may consist of coding tree units contained in more than one sliceand a slice may consist of coding tree units contained in more than onetile. However, ITU-T H.265 provides that one or both of the followingconditions shall be fulfilled: (1) All coding tree units in a slicebelong to the same tile; and (2) All coding tree units in a tile belongto the same slice. Tile sets may be used to define boundaries for codingdependencies (e.g., intra-prediction dependencies, entropy encodingdependencies, etc.,) and as such, may enable parallelism in coding.

In ITU-T H.265, a coded video sequence (CVS) may be encapsulated (orstructured) as a sequence of access units, where each access unitincludes video data structured as network abstraction layer (NAL) units.In ITU-T H.265, a bitstream is described as including a sequence of NALunits forming one or more CVSs. It should be noted that ITU-T H.265supports multi-layer extensions, including format range extensions(RExt), scalability (SHVC), multi-view (MV-HEVC), and 3-D (3D-HEVC).Multi-layer extensions enable a video presentation to include a baselayer and one or more additional enhancement layers. For example, a baselayer may enable a video presentation having a basic level of quality(e.g., High Definition rendering) to be presented and an enhancementlayer may enable a video presentation having an enhanced level ofquality (e.g., an Ultra High Definition rendering) to be presented. InITU-T H.265, an enhancement layer may be coded by referencing a baselayer. That is, for example, a picture in an enhancement layer may becoded (e.g., using inter prediction techniques) by referencing one ormore pictures (including scaled versions thereof) in a base layer. InITU-T H.265, each NAL unit may include an identifier indicating a layerof video data the NAL unit is associated with. It should be noted thatsub-bitstream extraction may refer to a process where a device receivinga compliant bitstream forms a new compliant bitstream by discardingand/or modifying data in the received bitstream. For example,sub-bitstream extraction may be used to form a new compliant bitstreamcorresponding to a particular representation of video (e.g., a highquality representation).

Referring to the example illustrated in FIG. 2 , each slice of videodata included in Pic₃ (i.e., Slice₁ and Slice₂) is illustrated as beingencapsulated in a NAL unit. In ITU-T H.265, each of a video sequence, aGOP, a picture, a slice, and CTU may be associated with metadata thatdescribes video coding properties. ITU-T H.265 defines parameters setsthat may be used to describe video data and/or video coding properties.In ITU-T H.265, parameter sets may be encapsulated as a special type ofNAL unit or may be signaled as a message. NAL units including codedvideo data (e.g., a slice) may be referred to as VCL (Video CodingLayer) NAL units and NAL units including metadata (e.g., parameter sets)may be referred to as non-VCL NAL units. Further, ITU-T H.265 enablessupplemental enhancement information (SEI) messages to be signaled. InITU-T H.265, SEI messages assist in processes related to decoding,display or other purposes, however, SEI messages may not be required forconstructing the luma or chroma samples by the decoding process. InITU-T H.265, SEI messages may be signaled in a bitstream using non-VCLNAL units. Further, SEI messages may be conveyed by some means otherthan by being present in the bitstream (i.e., signaled out-of-band).

FIG. 3 illustrates an example of a bitstream including multiple CVSs,where a CVS is represented by NAL units included in a respective accessunit. In the example illustrated in FIG. 3 , non-VCL NAL units includerespective parameter set units (i.e., Video Parameter Sets (VPS),Sequence Parameter Sets (SPS), and Picture Parameter Set (PPS) units)and an access unit delimiter NAL unit. ITU-T H.265 defines NAL unitheader semantics that specify the type of Raw Byte Sequence Payload(RBSP) data structure included in the NAL unit.

As described above, for inter prediction coding, reference samples in apreviously coded picture are used for coding video blocks in a currentpicture. Previously coded pictures which are available for use asreference when coding a current picture are referred as referencepictures. It should be noted that the decoding order does not necessarycorrespond with the picture output order, i.e., the temporal order ofpictures in a video sequence. In ITU-T H.265, when a picture is decodedit is stored to a decoded picture buffer (DPB) (which may be referred toas frame buffer, a reference buffer, a reference picture buffer, or thelike). In ITU-T H.265, pictures stored to the DPB are removed from theDPB when they been output and are no longer needed for coding subsequentpictures. In ITU-T H.265, a determination of whether pictures should beremoved from the DPB is invoked once per picture, after decoding a sliceheader, i.e., at the onset of decoding a picture. For example, referringto FIG. 2 , Pic₃ is illustrated as referencing Pic₂. Similarly, Pic₄ isillustrated as referencing Pic₁. With respect to FIG. 2 assuming thepicture number corresponds to the decoding order the DPB would bepopulated as follows: after decoding Pic₁, the DPB would include {Pic₁};at the onset of decoding Pic₂, the DPB would include {Pic₁}; afterdecoding Pic₂, the DPB would include {Pic₁, Pic₂}; at the onset ofdecoding Pic₃, the DPB would include {Pic₁, Pic₂}. Pic₃ would then bedecoded with reference to Pic₂ and after decoding Pic₃, the DPB wouldinclude {Pic₁, Pic₂, Pic₃}. At the onset of decoding Pic₄, pictures Pic₂and Pic₃ would be marked for removal from the DPB, as they are notneeded for decoding Pic₄ (or any subsequent pictures, not shown) andassuming Pic₂ and Pic₃ have been output, the DPB would be updated toinclude {Pic₁}. Pic₄ would then be decoded with referencing Pic-₁. Theprocess of marking pictures for removal from a DPB may be referred to asreference picture set (RPS) management.

In ITU-T H.265, the RPS of the current picture consists of five RPSlists: RefPicSetStCurrBefore, RefPicSetStCurrAfter, RefPicSetStFoll,RefPicSetLtCurr and RefPicSetLtFoll. RefPicSetStCurrBefore,RefPicSetStCurrAfter and RefPicSetStFoll are collectively referred to asthe short-term RPS. RefPicSetLtCurr and RefPicSetLtFoll are collectivelyreferred to as the long-term RPS. It should be noted that in ITU-T H.265and RefPicSetStCurrBefore, RefPicSetStCurrAfter and RefPicSetLtCurrcontain all reference pictures that may be used for inter prediction ofthe current picture and one or more pictures that follow the currentpicture in decoding order. RefPicSetStFoll and RefPicSetLtFoll consistof all reference pictures that are not used for inter prediction of thecurrent picture but may be used in inter prediction for one or morepictures that follow the current picture in decoding order. ITU-T H.265provides where each coded picture is associated with a picture ordercount variable, denoted as PicOrderCntVal. In ITU-T H.265, picture ordercounts are used to identify pictures. In ITU-T H.265, in one CVS, thePicOrderCntVal values for each of the coded pictures is unique. Further,in ITU-T H.265 picture order counts provide the relative output order ofpictures (i.e., from a decoded picture buffer, e.g., for display)included in a CVS (i.e., pictures with lower picture order counts areoutput before pictures with a higher picture order counts). In ITU-TH.265, the value of PicOrderCntVal is in the range of −2³¹ to 2³¹⁻¹inclusive. ITU-T H.265 provides where syntax explicitly identifies whichpictures are to be included in the RPS, as opposed to indicating whichpictures are to be included in the RPS implicitly by identifying whichpictures are to be removed from the DPB.

As described above, ITU-T H.265 provides two general types of referencepictures sets: long-term reference picture sets and short-term referencepicture sets. Thus, ITU-T H.265 provides where pictures in the DPB aremarked as follows: “unused for reference,” “used for short-termreference,” or “used for long-term reference.” In ITU-T H.265,short-term reference pictures are identified by their PicOrderCntValvalues and long-term reference pictures are identified either by theirPicOrderCntVal values or their slice_pic_order_cnt_lsb values (describedbelow). ITU-T H.265 further provides where the following five lists ofpicture order count values are constructed to derive the RPS:PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll. Theconstruction of PocStCurrBefore, PocStCurrAfter, PocStFoll, PocLtCurrand PocLtFoll is described in further detail below.

In ITU-T H.265, a set of long-term RPS may be signaled in an SPS.Further, in ITU-T sets of candidate short-term RPSs may be in signaledin the SPS. Further, one of the candidate short-term RPSs may beindicated by signaling of an index to one of the SPS candidate RPSs inthe slice segment header. Further, short-term RPS may be signaleddirectly in slice segment header.

Table 1 illustrates the portion of the sequence parameter set in ITU-TH.265 relating to indicating reference picture sets.

TABLE 1 seq_parameter_set( ) { Descriptor ... num_short_term_ref_pic_sets ue(v)  for( i = 0; i <num_short_term_ref_pic_sets; i++)   st_ref_pic_set( i ) long_term_ref_pic_present_flag u(1)  if(long_term_ref_pics_present_flag ) {   num_long_term_ref_pic_sps ue(v)  for( i = 0; i < num_long_term_ref_pic_sets; i++)   lt_ref_pic_poc_lsb_sps[ i ] u(v)    used_by_curr_pic_lt_sps_flag[ i ]u(1)   }  } ...

-   -   ITU-T H.265 provides the following definitions for the        respective syntax elements illustrated in Table 1.    -   num_short_term_ref_pic_sets specifies the number of        st_ref_pic_set( ) syntax structures included in the SPS. The        value of num_short_term_ref_pic_sets shall be in the range of 0        to 64, inclusive.    -   long_term_ref_pics_present_flag equal to 0 specifies that no        long-term reference picture is used for inter prediction of any        coded picture in the CVS. long_term_ref_pics_present_flag equal        to 1 specifies that long-term reference pictures may be used for        inter prediction of one or more coded pictures in the CVS.    -   num_long_term_ref_pics_sps specifies the number of candidate        long-term reference pictures that are specified in the SPS. The        value of num_long_term_ref_pics_sps shall be in the range of 0        to 32, inclusive.    -   lt_ref_pic_poc_lsb_sps[i] specifies the picture order count        modulo MaxPicOrderCntLsb of the i-th candidate long-term        reference picture specified in the SPS. The number of bits used        to represent lt_ref_pic_pocisb_sps[i] is equal to        log2_max_pic_order_cnt_lsb_minus4+4.    -   used_by_curr_pic_lt_sps_flag[i] equal to 0 specifies that the        i-th candidate long-term reference picture specified in the SPS        is not used for reference by a picture that includes in its        long-term reference picture set (RPS) the i-th candidate        long-term reference picture specified in the SPS.

With respect to st_ref_pic_set (i), Table 2 illustrates thest_ref_pic_set(i) syntax provided in ITU-T H.265.

TABLE 2 st_ref_pic_set( stRpsIdx ) { Descriptor  if( stRpsIdx != 0 )  inter_ref_pic_set_prediction_flag u(1)  if(inter_ref_pic_set_prediction_flag ) {   if( stRpsIdx ==num_short_term_ref_pic_sets )    delta_idx_minus1 ue(v)   delta_rps_signu(1)   abs_delta_rps_minus1 ue(v)   for( j = 0; j <= NumDeltaPocs[RefRpsIdx ]; j++ ) {    used_by_curr_pic_flag[ j ] u(1)    if(!used_by_curr_pic_flag[ j ] )     use_delta_flag[ j ] u(1)   }  } else {  num_negative_pics ue(v)   num_positive_pics ue(v)   for( i = 0; i <num_negative_pics; i++ ) {    delta_poc_s0_minus1[ i ] ue(v)   used_by_curr_pic_s0_flag[ i ] u(1)   }   for( i = 0; i <num_positive_pics; i++ ) {    delta_poc_s1_minus1[ i ] ue(v)   used_by_curr_pic_s1_flag[ i ] u(1)   }  } }

-   -   ITU-T H.265 provides the following definitions for the        respective syntax elements illustrated in Table 2.    -   inter_ref_pic_set_prediction_flag equal to 1 specifies that the        stRpsIdx-th candidate short-term RPS is predicted from another        candidate short-term RPS, which is referred to as the source        candidate short-term RPS. When inter_ref_pic_set_prediction_flag        is not present, it is inferred to be equal to 0.    -   delta_idx_minus1 plus 1 specifies the difference between the        value of stRpsIdx and the index, into the list of the candidate        short-term RPSs specified in the SPS, of the source candidate        short-term RPS. The value of delta_idx_minus1 shall be in the        range of 0 to stRpsIdx−1, inclusive. When delta_idx_minus1 is        not present, it is inferred to be equal to 0.

The variable RefRpsIdx is derived as follows:

RefRpsIdx=stRpsIdx−(delta_idx_minus1+1)

-   -   delta_rps_sign and abs_delta_rps_minus1 together specify the        value of the variable deltaRps as follows:

deltaRps=(1−2*delta_rps_sign)*(abs_delta_rps_minus1+1)

The variable deltaRps represents the value to be added to the pictureorder count difference values of the source candidate short-term RPS toobtain the picture order count difference values of the stRpsIdx-thcandidate short-term RPS. The value of abs_delta_rps_minus1 shall be inthe range of 0 to 2¹⁵-1, inclusive.

-   -   used_by_curr_pic_flag[j] equal to 0 specifies that the j-th        entry in the source candidate short-term RPS is not used for        reference by the current picture.    -   use_delta_flag[j] equal to 1 specifies that the j-th entry in        the source candidate short-term RPS is included in the        stRpsIdx-th candidate short-term RPS. use_delta_flag[j] equal to        0 specifies that the j-th entry in the source candidate        short-term RPS is not included in the stRpsIdx-th candidate        short-term RPS. When use_delta_flag[j] is not present, its value        is inferred to be equal to 1.

When inter_ref_pic_set_prediction_flag is equal to 1, the variablesDeltaPocS0[stRpsIdx][i], UsedByCurrPicS0[stRpsIdx][i],NumNegativePics[stRpsIdx], DeltaPocS1[stRpsIdx][i],UsedByCurrPicS1[stRpsIdx][i] and NumPositivePics[stRpsIdx] are derivedas follows:

i = 0 for( j = NumPositivePics[ RefRpsIdx ] − 1; j >= 0; j− − ) {  dPoc= DeltaPocS1[ RefRpsIdx ][ j ] + deltaRps  if( dPoc <0 && use_delta_flag[ NumNegativePics[ RefRpsIdx ] + j ] ) {  DeltaPocS0[ stRpsIdx ][ i ] = dPoc  UsedByCurrPicS0[  stRpsIdx  ][  i++  ]  = used_by_curr_pic_flag[NumNegativePics[ RefRpsIdx ] + j ]  } } if( deltaRps <0 && use_delta_flag[ NumDeltaPocs[ RefRpsIdx ] ] ) { DeltaPocS0[stRpsIdx ][ i ] = deltaRps  UsedByCurrPicS0[  stRpsIdx  ][  i++  ]  =used_by_curr_pic_flag[ NumDeltaPocs[ RefRpsIdx ] ] } for( j = 0; j <NumNegativePics[ RefRpsIdx ]; j++ ) {  dPoc = DeltaPocS0[ RefRpsIdx ][ j] + deltaRps  if( dPoc < 0 && use_delta_flag[ j ] ) {   DeltaPocS0[stRpsIdx ][ i ] = dPoc   UsedByCurrPicS0[ stRpsIdx ][ i++ ] =used_by_curr_pic_flag[ j ]  } } NumNegativePics[ stRpsIdx ] = i i = 0for( j = NumNegativePics[ RefRpsIdx ] − 1; j >= 0; j− − ) {  dPoc =DeltaPocS0[ RefRpsIdx ][ j ] + deltaRps  if( dPoc > 0 && use_delta_flag[j ] ) {   DeltaPocS1[ stRpsIdx ][ i ] = dPoc   UsedByCurrPicS1[ stRpsIdx][ i++ ] = used_by_curr_pic_flag[ j ]  } } if( deltaRps >0 && use_delta_flag[ NumDeltaPocs[ RefRpsIdx ] ] ) { DeltaPocS1[stRpsIdx ][ i ] = deltaRps  UsedByCurrPicS1[  stRpsIdx  ][  i++  ]  =used_by_curr_pic_flag[ NumDeltaPocs[ RefRpsIdx ] ] } for( j = 0; j <NumPositivePics[ RefRpsIdx ]; j++) {  dPoc = DeltaPocS1[ RefRpsIdx ][ j] + deltaRps  if( dPoc > 0 && use_delta_flag[ NumNegativePics[ RefRpsIdx] + j ] ) {   DeltaPocS1[ stRpsIdx ][ i ] = dPoc  UsedByCurrPicS1[  stRpsIdx  ][  i++  ]  = used_by_curr_pic_flag[NumNegativePics[ RefRpsIdx ] + j ]  } } NumPositivePics[ stRpsIdx ] = i

-   -   num_negative_pics specifies the number of entries in the        stRpsIdx-th candidate short-term RPS that have picture order        count values less than the picture order count value of the        current picture. When nuh_layer_id of the current picture is        equal to 0, the value of num_negative_pics shall be in the range        of 0 to        sps_max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1],        inclusive.    -   num_positive_pics specifies the number of entries in the        stRpsIdx-th candidate short-term RPS that have picture order        count values greater than the picture order count value of the        current picture. When nuh_layer_id of the current picture is        equal to 0, the value of num_positive_pics shall be in the range        of 0 to        sps_max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1]−num_negative_pics,        inclusive.    -   delta_poc_s0_minus1[i] plus 1, when i is equal to 0, specifies        the difference between the picture order count values of the        current picture and i-th entry in the stRpsIdx-th candidate        short-term RPS that has picture order count value less than that        of the current picture, or, when i is greater than 0, specifies        the difference between the picture order count values of the        (i−1)-th entry and the i-th entry in the stRpsIdx-th candidate        short-term RPS that have picture order count values less than        the picture order count value of the current picture. The value        of delta_poc_s0_minus1[i] shall be in the range of 0 to 2¹⁵-1,        inclusive.    -   used_by_curr_pic_s0_flag[i] equal to 0 specifies that the i-th        entry in the stRpsIdx-th candidate short-term RPS that has        picture order count value less than that of the current picture        is not used for reference by the current picture.    -   delta_poc_s1_minus1[i] plus 1, when i is equal to 0, specifies        the difference between the picture order count values of the        current picture and the i-th entry in the stRpsIdx-th candidate        short-term RPS that has picture order count value greater than        that of the current picture, or, when i is greater than 0,        specifies the difference between the picture order count values        of the i-th entry and the (i−1)-th entry in the current        candidate short-term RPS that have picture order count values        greater than the picture order count value of the current        picture. The value of delta_poc_s1_minus1[i] shall be in the        range of 0 to 2¹⁵-1, inclusive.

used by_curr_pic_s1_flag[i] equal to 0 specifies that the i-th entry inthe current candidate short-term RPS that has picture order count valuegreater than that of the current picture is not used for reference bythe current picture.

When inter_ref_pic_set_prediction_flag is equal to 0, the variablesNumNegativePics[stRpsIdx], NumPositivePics[stRpsIdx],UsedByCurrPicS0[stRpsIdx][i], UsedByCurrPicS1[stRpsIdx][i],DeltaPocS0[stRpsIdx][i] and DeltaPocS1[stRpsIdx][i] are derived asfollows:

NumNegativePics[ stRpsIdx ] = num_negative_pics NumPositivePics[stRpsIdx ] = num_positive_pics UsedByCurrPicS0[ stRpsIdx ][ i ] =used_by_curr_pic_s0_flag[ i ] UsedByCurrPicS1[ stRpsIdx ][ i ] =used_by_curr_pic_s1_flag[ i ] -  If i is equal to 0, the followingapplies:  DeltaPocS0[ stRpsIdx ][ i ] = −( delta_poc_s0_minus1[ i ] + 1)  DeltaPocS1[ stRpsIdx ][ i ] = delta_poc_s1_minus1[ i ] + 1 - Otherwise, the following applies: DeltaPocS0[ stRpsIdx ][ i ] = DeltaPocS0[ stRpsIdx ][ i − 1 ] − (delta_poc_s0_minus1[ i ] + 1 ) DeltaPocS1[ stRpsIdx ][ i ] = DeltaPocS1[  stRpsIdx ][ i − 1 ] + (delta_poc_s1_minus1[ i ] + 1 )

The variable NumDeltaPocs[stRpsIdx] is derived as follows:

 NumDeltaPocs[ stRpsIdx ]  =  NumNegativePics[ stRpsIdx ]  +NumPositivePics[ stRpsIdx ]

As described above, ITU-T H.265 specifies where ast_ref_pic_set(stRpsIdx) syntax structure may be present in an SPS or ina slice segment header. ITU-T H.265 further provides where depending onwhether the syntax structure is included in a slice header or an SPS,the following applies:

-   -   If present in a slice header, the st_ref_pic_set(stRpsIdx)        syntax structure specifies the short-term RPS of the current        picture (the picture containing the slice), and the following        applies:        -   The content of the st_ref_pic_set(stRpsIdx) syntax structure            shall be the same in all slice headers of the current            picture.        -   The value of stRpsIdx shall be equal to the syntax element            num_short_term_ref_pic_sets in the active SPS.        -   The short-term RPS of the current picture is also referred            to as the num_short_term_ref_pic_sets-th candidate            short-term RPS in the semantics specified in the remainder            of this clause.        -   Otherwise (present in an SPS), the st_ref_pic_set(stRpsIdx)            syntax structure specifies a candidate short term RPS, and            the term “the current picture” in the semantics specified in            the remainder of this clause refers to each picture that has            short_term_ref_pic_set_idx equal to stRpsIdx in a CVS that            has the SPS as the active SPS.

Table 3 illustrates the portion of the slice segment header in ITU-TH.265 relating to indicating reference picture sets.

TABLE 3 slice_segment_header( ) { Descriptor ...   if( nal_unit_type !=IDR_W_RADL && nal_unit_type != IDR_N_LP ) {    slice_pic_order_cnt_lsbu(v)    short_term_ref_pic_set_sps_flag u(1)    if(!short_term_ref_pic_set_sps_flag )     st_ref_pic_set(num_short_term_ref_pic_sets )    else if( num_short_term_ref_pic_sets >1 )     short_term_ref_pic_set_idx u(v)    if(long_term_ref_pics_present_flag ) {     if( num_long_term_ref_pics_sps >0 )      num_long_term_sps ue(v)     num_long_term_pics ue(v)     for( i= 0; i < num_long_term_sps +     num_long_term_pics; i++ ) {      if( i< num_long_term_sps ) {       if( num_long_term_ref_pics_sps > l )       lt_idx_sps[ i ] u(v)      } else {       poc_lsb_lt[ i ] u(v)      used_by_curr_pic_lt_flag[ i ] u(1)      }     delta_poc_msb_present_flag[ i ] u(1)      if(delta_poc_msb_present_flag[ i ] )       delta_poc_msb_cycle_lt[ i ]ue(v)     }    } ...

-   -   ITU-T H.265 provides the following definitions for the        respective syntax elements illustrated in Table 3.    -   slice_pic_order_cnt_lsb specifies the picture order count modulo        MaxPicOrderCntLsb for the current picture. The length of the        slice_pic_order_cnt_lsb syntax element is        log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of the        slice_pic_order_cnt_lsb shall be in the range of 0 to        MaxPicOrderCntLsb−1, inclusive. When slice_pic_order_cnt_lsb is        not present, slice_pic_order_cnt_lsb is inferred to be equal to        0, except in some case specificed in ITU-H.265.    -   short_term_ref_pic_set_sps_flag equal to 1 specifies that the        short-term RPS of the current picture is derived based on one of        the st_ref_pic_set( ) syntax structures in the active SPS that        is identified by the syntax element short_term_ref_pic_set_idx        in the slice header. short_term_ref_pic_set_sps_flag equal to 0        specifies that the short-term RPS of the current picture is        derived based on the st_ref_pic_set( ) syntax structure that is        directly included in the slice headers of the current picture.        When num_short_term_ref_pic_sets is equal to 0, the value of        short_term_ref_pic_set_sps_flag shall be equal to 0.    -   short_term_ref_pic_set_idx specifies the index, into the list of        the st_ref_pic_set( ) syntax structures included in the active        SPS, of the st_ref_pic_set( ) syntax structure that is used for        derivation of the short-term RPS of the current picture. The        syntax element short_term_ref_pic_set_idx is represented by        Ceil(Log2(num_short_term_ref_pic_sets)) bits. When not present,        the value of short_term_ref_pic_set_idx is inferred to be equal        to 0. The value of short_term_ref_pic_set_idx shall be in the        range of 0 to num_short_term_ref_pic_sets−1, inclusive.    -   The variable CurrRpsIdx is derived as follows:        -   If short_term_ref_pic_set_sps_flag is equal to 1, CurrRpsIdx            is set equal to shorttermref_pic_set_idx.        -   Otherwise, CurrRpsIdx is set equal to            nunam_short_termref_pic_sets.    -   num_long_term_sps specifies the number of entries in the        long-term RPS of the current picture that are derived based on        the candidate long-term reference pictures specified in the        active SPS. The value of num_long_term_sps shall be in the range        of 0 to num_long_term_ref_pics_sps, inclusive. When not present,        the value of num_long_term_sps is inferred to be equal to 0.    -   num_long_term_pics specifies the number of entries in the        long-term RPS of the current picture that are directly signalled        in the slice header. When not present, the value of        num_long_term_pics is inferred to be equal to 0.    -   When nuh_layer_id is equal to 0, the sum of        NumNegativePics[CurrRpsIdx], NumPositivePics[CurrRpsIdx],        num_long_term_sps and num_long_term_pics shall be less than or        equal to sps_max_dec_pic_buffering        minus1[sps_max_sub_layers_minus1].    -   lt_idx_sps[i] specifies an index, into the list of candidate        long-term reference pictures specified in the active SPS, of the        i-th entry in the long-term RPS of the current picture. The        number of bits used to represent lt_idx_sps[i] is equal to        Ceil(Log2(num_long_term_ref_pics_sps)). When not present, the        value of lt_idx_sps[i] is inferred to be equal to 0. The value        of lt_idx_sps[i] shall be in the range of 0 to        num_long_term_ref_pics_sps−1, inclusive.    -   poc_lsb_lt[i] specifies the value of the picture order count        modulo MaxPicOrderCntLsb of the i-th entry in the long-term RPS        of the current picture. The length of the poc_lsb_lt[i] syntax        element is log2_max_pic_order_cnt_lsb_minus4+4 bits.    -   used_by_curr_pic_h_flag[i] equal to 0 specifies that the i-th        entry in the long-term RPS of the current picture is not used        for reference by the current picture. The variables PocLsbLt[i]        and UsedByCurrPicLt[i] are derived as follows:        -   If i is less than num_long_term_sps, PocLsbLt[i] is set            equal to lt_ref_pic_poc_lsb_sps[lt_idx_sps[i]] and            UsedByCurrPicLt[i] is set equal to            used_by_curr_pic_h_sps_flag[lt_idx_sps[i]].        -   Otherwise, PocLsbLt[i] is set equal to poc_lsb_lt[i] and            UsedByCurrPicLt[i] is set equal to            used_by_curr_pic_lt_flag[i].    -   delta_poc_msb_present_flag[i] equal to 1 specifies that        delta_poc_msb_cycle_lt[i] is present.        delta_poc_msb_present_flag[i] equal to 0 specifies that        delta_poc_msb_cycle_lt[i] is not present.    -   delta_poc_msb_cycle_lt[i] is used to determine the value of the        most significant bits of the picture order count value of the        i-th entry in the long-term RPS of the current picture. When        delta_poc_msb_cycle_lt[i] is not present, it is inferred to be        equal to 0.

The variable DeltaPocMsbCycleLt[i] is derived as follows:

  if( i == 0 | | i = = num_long_term_sps )  DeltaPocMsbCycleLt[ i ] =delta_poc_msb_cycle_lt[ i ] else  DeltaPocMsbCycleLt[ i ] =delta_poc_msb_cycle_lt[ i ] + DeltaPocMsbCycleLt[ i − 1 ]

-   -   As described above, in ITU-T H.265 PocStCurrBefore,        PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll are        constructed to derive the RPS. ITU-T H.265 provides the        following with respect to constructing PocStCurrBefore,        PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll:        -   If the current picture is an IDR picture, PocStCurrBefore,            PocStCurrAfter, PocStFoll, PocLtCurr and PocLtFoll are all            set to be empty, and NumPocStCurrBefore, NumPocStCurrAfter,            NumPocStFoll, NumPocLtCurr and NumPocLtFoll are all set            equal to 0.        -   Otherwise, the following applies:

 for( i = 0, j = 0, k = 0; i < NumNegativePics[ CurrRpsIdx ] ;i++ )  if( UsedByCurrPicS0[ CurrRpsIdx ][ i ] )   PocStCurrBefore[ j++ ] =PicOrderCntVal + DeltaPocS0[ CurrRpsIdx ][ i ]   else   PocStFoll[ k++ ]= PicOrderCntVal + DeltaPocS0[ CurrRpsIdx ] [ i ]  NumPocStCurrBefore =j  for( i = 0, j = 0; i < NumPositivePics[ CurrRpsIdx ]; i++ )   if(UsedByCurrPicS1[ CurrRpsIdx ][ i ] )   PocStCurrAfter[j++] =PicOrderCntVal + DeltaPocS1[ CurrRpsIdx ][ i ]   else   PocStFoll[ k++ ]= PicOrderCntVal + DeltaPocS1[ CurrRpsIdx ][ i ]  NumPocStCurrAfter = j NumPocStFoll = k  for( i = 0, j = 0, k = 0; i < num_long_term_sps +num_long_term_pics; i++ ) {   pocLt = PocLsbLt[ i ]   if(delta_poc_msb_present_flag[ i ] )   pocLt += PicOrderCntVal − DeltaPocMsbCycleLt[ i ] *  MaxPicOrderCntLsb − ( PicOrderCntVal & (MaxPicOrderCntLsb − 1 ) )  if( UsedByCurrPicLt[ i ] ) {    PocLtCurr[ j ] =pocLt   CurrDeltaPocMsbPresentFlag[  j++  ]  =   delta_poc_msb_present_flag[i ]   } else {    PocLtFoll[ k ] = pocLt   FollDeltaPocMsbPresentFlag[  k++  ]  =   delta_poc_msb_present_flag[i ]    } } NumPocLtCurr = j NumPocLtFoll = k

-   -   ITU-T H.265 further provides where PocStCurrBefore,        PocStCurrAfter, PocStFoll, PocLtCurr, and PocLtFoll are used to        derive the five RPS lists for the current picture        (RefPicSetStCurrBefore, RefPicSetStCurrAfter, RefPicSetStFoll,        RefPicSetLtCurr and RefPicSetLtFoll) as follows:        -   1. The following applies:

for( i = 0; i < NumPocLtCurr; i++ )  if( !CurrDeltaPocMsbPresentFlag[ i] )   if( there is a reference picture picX in the DPB withPicOrderCntVal & ( MaxPicOrderCntLsb − 1 )     equal to PocLtCurr[ i ]and nuh_layer_id equal to currPicLayerId)    RefPicSetLtCurr[ i ] = picX  else    RefPicSetLtCurr[ i ] = “no reference picture”  else   if(there is a reference picture picX in the DPB with PicOrderCntVal equalto PocLtCurr[ i ]     and nuh_layer_id equal to currPicLayerId )   RefPicSetLtCurr[ i ] = picX   else    RefPicSetLtCurr[ i ] = “noreference picture” for( i = 0; i < NumPocLtFoll; i++ )  if(!FollDeltaPocMsbPresentFlag[ i ] )   if( there is a reference picturepicX in the DPB with PicOrderCntVal & (MaxPicOrderCntLsb − 1 )     equalto PocLtFoll[ i ] and nuh_layer_id equal to currPicLayerId )   RefPicSetLtFoll[ i ] = picX   else    RefPicSetLtFoll[ i ] = “noreference picture” else   if( there is a reference picture picX in theDPB with PicOrderCntVal equal to PocLtFoll[ i ]     and nuh_layer_idequal to currPicLayerId )    RefPicSetLtFoll[ i ] = picX   else   RefPicSetLtFoll[ i ] = “no reference picture”

-   -   -   2. All reference pictures that are included in            RefPicSetLtCurr or RefPicSetLtFoll and have nuh_layer_id            equal to currPicLayerId are marked as “used for long-term            reference”.        -   3. The following applies:

for( i = 0; i < NumPocStCurrBefore; i++ )  if( there is a short-termreference picture picX in the DPB    with PicOrderCntVal equal toPocStCurrBefore[ i ] and nuh_layer_id equal to currPicLayerId )  RefPicSetStCurrBefore[ i ] = picX  else   RefPicSetStCurrBefore[ i ] =“no reference picture” for( i = 0; i < NumPocStCurrAfter; i++ )  if(there is a short-term reference picture picX in the DPB    withPicOrderCntVal equal to PocStCurrAfter[ i ] and nuh_layer_id equal tocurrPicLayerId )   RefPicSetStCurrAfter[ i ] = picX  else  RefPicSetStCurrAfter[ i ] = “no reference picture” for( i = 0; i <NumPocStFoll; i++ )  if( there is a short-term reference picture picX inthe DPB    with PicOrderCntVal equal to PocStFoll[ i ] and nuh_layer_idequal to currPicLayerId )   RefPicSetStFoll[ i ] = picX  else  RefPicSetStFoll[ i ] = “no reference picture”

-   -   -   4. All reference pictures in the DPB that are not included            in RefPicSetLtCurr, RefPicSetLtFoll, RefPicSetStCurrBefore,            RefPicSetStCurrAfter, or RefPicSetStFoll and have            nuh_layer_id equal to currPicLayerId are marked as “unused            for reference”.

Finally, in ITU-T H.265 a decoding process is performed for constructionof one or two temporary reference picture list(s) using the five RPSlists. The one or two temporary reference picture list(s) that areconstructed may optionally be modified (i.e., re-indexed). The modifiedor unmodified temporary reference picture list(s) are used to create afinal reference picture list(s). The index values of the referencepicture list(s) are used to identify a picture during inter prediction.

According to the techniques herein, a simplified process for generatinga reference picture lists is described. According to the techniquesherein, reference picture lists may be signaled directly. As describedin further detail below, in one example, according to the techniquesherein, reference picture lists may be signaled directly as follows: aset of candidate picture lists may be signaled in the SPS and one tothree indices to the SPS candidate picture lists may be signaled in theslice segment header or new reference picture lists may be signaleddirectly in slice segment header; the one or two final reference picturelists may be created based on the signaled indices. Additionally,reference pictures are marked based on one, two, or three referencepicture lists. The techniques described herein result is a moresimplified decoding process compared to the ITU-T H.265 approach.Further, direct signaling of reference picture lists avoids requiringsignaling of reference picture list modification syntax on top ofreference picture set syntax.

FIG. 1 is a block diagram illustrating an example of a system that maybe configured to code (i.e., encode and/or decode) video data accordingto one or more techniques of this disclosure. System 100 represents anexample of a system that may encapsulate video data according to one ormore techniques of this disclosure. As illustrated in FIG. 1 , system100 includes source device 102, communications medium 110, anddestination device 120. In the example illustrated in FIG. 1 , sourcedevice 102 may include any device configured to encode video data andtransmit encoded video data to communications medium 110. Destinationdevice 120 may include any device configured to receive encoded videodata via communications medium 110 and to decode encoded video data.Source device 102 and/or destination device 120 may include computingdevices equipped for wired and/or wireless communications and mayinclude, for example, set top boxes, digital video recorders,televisions, desktop, laptop or tablet computers, gaming consoles,medical imagining devices, and mobile devices, including, for example,smartphones, cellular telephones, personal gaming devices.

Communications medium 110 may include any combination of wireless andwired communication media, and/or storage devices. Communications medium110 may include coaxial cables, fiber optic cables, twisted pair cables,wireless transmitters and receivers, routers, switches, repeaters, basestations, or any other equipment that may be useful to facilitatecommunications between various devices and sites. Communications medium110 may include one or more networks. For example, communications medium110 may include a network configured to enable access to the World WideWeb, for example, the Internet. A network may operate according to acombination of one or more telecommunication protocols.Telecommunications protocols may include proprietary aspects and/or mayinclude standardized telecommunication protocols. Examples ofstandardized telecommunications protocols include Digital VideoBroadcasting (DVB) standards, Advanced Television Systems Committee(ATSC) standards, Integrated Services Digital Broadcasting (ISDB)standards, Data Over Cable Service Interface Specification (DOCSIS)standards, Global System Mobile Communications (GSM) standards, codedivision multiple access (CDMA) standards, 3rd Generation PartnershipProject (3GPP) standards, European Telecommunications StandardsInstitute (ETSI) standards, Internet Protocol (IP) standards, WirelessApplication Protocol (WAP) standards, and Institute of Electrical andElectronics Engineers (IEEE) standards.

Storage devices may include any type of device or storage medium capableof storing data. A storage medium may include a tangible ornon-transitory computer-readable media. A computer readable medium mayinclude optical discs, flash memory, magnetic memory, or any othersuitable digital storage media. In some examples, a memory device orportions thereof may be described as non-volatile memory and in otherexamples portions of memory devices may be described as volatile memory.Examples of volatile memories may include random access memories (RAM),dynamic random access memories (DRAM), and static random access memories(SRAM). Examples of non-volatile memories may include magnetic harddiscs, optical discs, floppy discs, flash memories, or forms ofelectrically programmable memories (EPROM) or electrically erasable andprogrammable (EEPROM) memories. Storage device(s) may include memorycards (e.g., a Secure Digital (SD) memory card), internal/external harddisk drives, and/or internal/external solid state drives. Data may bestored on a storage device according to a defined file format.

FIG. 4 is a conceptual drawing illustrating an example of componentsthat may be included in an implementation of system 100. In the exampleimplementation illustrated in FIG. 4 , system 100 includes one or morecomputing devices 402A-402N, television service network 404, televisionservice provider site 406, wide area network 408, local area network410, and one or more content provider sites 412A-412N. Theimplementation illustrated in FIG. 4 represents an example of a systemthat may be configured to allow digital media content, such as, forexample, a movie, a live sporting event, etc., and data and applicationsand media presentations associated therewith to be distributed to andaccessed by a plurality of computing devices, such as computing devices402A-402N. In the example illustrated in FIG. 4 , computing devices402A-402N may include any device configured to receive data from one ormore of television service network 404, wide area network 408, and/orlocal area network 410. For example, computing devices 402A-402N may beequipped for wired and/or wireless communications and may be configuredto receive services through one or more data channels and may includetelevisions, including so-called smart televisions, set top boxes, anddigital video recorders. Further, computing devices 402A-402N mayinclude desktop, laptop, or tablet computers, gaming consoles, mobiledevices, including, for example, “smart” phones, cellular telephones,and personal gaming devices.

Television service network 404 is an example of a network configured toenable digital media content, which may include television services, tobe distributed. For example, television service network 404 may includepublic over-the-air television networks, public or subscription-basedsatellite television service provider networks, and public orsubscription-based cable television provider networks and/or over thetop or Internet service providers. It should be noted that although insome examples television service network 404 may primarily be used toenable television services to be provided, television service network404 may also enable other types of data and services to be providedaccording to any combination of the telecommunication protocolsdescribed herein. Further, it should be noted that in some examples,television service network 404 may enable two-way communications betweentelevision service provider site 406 and one or more of computingdevices 402A-402N. Television service network 404 may comprise anycombination of wireless and/or wired communication media. Televisionservice network 404 may include coaxial cables, fiber optic cables,twisted pair cables, wireless transmitters and receivers, routers,switches, repeaters, base stations, or any other equipment that may beuseful to facilitate communications between various devices and sites.Television service network 404 may operate according to a combination ofone or more telecommunication protocols. Telecommunications protocolsmay include proprietary aspects and/or may include standardizedtelecommunication protocols. Examples of standardized telecommunicationsprotocols include DVB standards, ATSC standards, ISDB standards, DTMBstandards, DMB standards, Data Over Cable Service InterfaceSpecification (DOCSIS) standards, HbbTV standards, W3C standards, andUPnP standards.

Referring again to FIG. 4 , television service provider site 406 may beconfigured to distribute television service via television servicenetwork 404. For example, television service provider site 406 mayinclude one or more broadcast stations, a cable television provider, ora satellite television provider, or an Internet-based televisionprovider. For example, television service provider site 406 may beconfigured to receive a transmission including television programmingthrough a satellite uplink/downlink. Further, as illustrated in FIG. 4 ,television service provider site 406 may be in communication with widearea network 408 and may be configured to receive data from contentprovider sites 412A-412N. It should be noted that in some examples,television service provider site 406 may include a television studio andcontent may originate therefrom.

Wide area network 408 may include a packet based network and operateaccording to a combination of one or more telecommunication protocols.Telecommunications protocols may include proprietary aspects and/or mayinclude standardized telecommunication protocols. Examples ofstandardized telecommunications protocols include Global System MobileCommunications (GSM) standards, code division multiple access (CDMA)standards, 3^(rd) Generation Partnership Project (3GPP) standards,European Telecommunications Standards Institute (ETSI) standards,European standards (EN), IP standards, Wireless Application Protocol(WAP) standards, and Institute of Electrical and Electronics Engineers(IEEE) standards, such as, for example, one or more of the IEEE 802standards (e.g., Wi-Fi). Wide area network 408 may comprise anycombination of wireless and/or wired communication media. Wide areanetwork 408 may include coaxial cables, fiber optic cables, twisted paircables, Ethernet cables, wireless transmitters and receivers, routers,switches, repeaters, base stations, or any other equipment that may beuseful to facilitate communications between various devices and sites.In one example, wide area network 408 may include the Internet. Localarea network 410 may include a packet based network and operateaccording to a combination of one or more telecommunication protocols.Local area network 410 may be distinguished from wide area network 408based on levels of access and/or physical infrastructure. For example,local area network 410 may include a secure home network.

Referring again to FIG. 4 , content provider sites 412A-412N representexamples of sites that may provide multimedia content to televisionservice provider site 406 and/or computing devices 402A-402N. Forexample, a content provider site may include a studio having one or morestudio content servers configured to provide multimedia files and/orstreams to television service provider site 406. In one example, contentprovider sites 412A-412N may be configured to provide multimedia contentusing the IP suite. For example, a content provider site may beconfigured to provide multimedia content to a receiver device accordingto Real Time Streaming Protocol (RTSP), HTTP, or the like. Further,content provider sites 412A-412N may be configured to provide data,including hypertext based content, and the like, to one or more ofreceiver devices computing devices 402A-402N and/or television serviceprovider site 406 through wide area network 408. Content provider sites412A-412N may include one or more web servers. Data provided by dataprovider site 412A-412N may be defined according to data formats.

Referring again to FIG. 1 , source device 102 includes video source 104,video encoder 106, data encapsulator 107, and interface 108. Videosource 104 may include any device configured to capture and/or storevideo data. For example, video source 104 may include a video camera anda storage device operably coupled thereto. Video encoder 106 may includeany device configured to receive video data and generate a compliantbitstream representing the video data. A compliant bitstream may referto a bitstream that a video decoder can receive and reproduce video datatherefrom. Aspects of a compliant bitstream may be defined according toa video coding standard. When generating a compliant bitstream videoencoder 106 may compress video data. Compression may be lossy(discernible or indiscernible to a viewer) or lossless. FIG. 5 is ablock diagram illustrating an example of video encoder 500 that mayimplement the techniques for encoding video data described herein. Itshould be noted that although example video encoder 500 is illustratedas having distinct functional blocks, such an illustration is fordescriptive purposes and does not limit video encoder 500 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video encoder 500 may be realized using anycombination of hardware, firmware, and/or software implementations.

Video encoder 500 may perform intra prediction coding and interprediction coding of picture areas, and, as such, may be referred to asa hybrid video encoder. In the example illustrated in FIG. 5 , videoencoder 500 receives source video blocks. In some examples, source videoblocks may include areas of picture that has been divided according to acoding structure. For example, source video data may includemacroblocks, CTUs, CBs, sub-divisions thereof, and/or another equivalentcoding unit. In some examples, video encoder 500 may be configured toperform additional sub-divisions of source video blocks. It should benoted that the techniques described herein are generally applicable tovideo coding, regardless of how source video data is partitioned priorto and/or during encoding. In the example illustrated in FIG. 5 , videoencoder 500 includes summer 502, transform coefficient generator 504,coefficient quantization unit 506, inverse quantization and transformcoefficient processing unit 508, summer 510, intra prediction processingunit 512, inter prediction processing unit 514, filter unit 516, andentropy encoding unit 518. As illustrated in FIG. 5 , video encoder 500receives source video blocks and outputs a bitstream.

In the example illustrated in FIG. 5 , video encoder 500 may generateresidual data by subtracting a predictive video block from a sourcevideo block. The selection of a predictive video block is described indetail below. Summer 502 represents a component configured to performthis subtraction operation. In one example, the subtraction of videoblocks occurs in the pixel domain. Transform coefficient generator 504applies a transform, such as a discrete cosine transform (DCT), adiscrete sine transform (DST), or a conceptually similar transform, tothe residual block or sub-divisions thereof (e.g., four 8×8 transformsmay be applied to a 16×16 array of residual values) to produce a set ofresidual transform coefficients. Transform coefficient generator 504 maybe configured to perform any and all combinations of the transformsincluded in the family of discrete trigonometric transforms, includingapproximations thereof. Transform coefficient generator 504 may outputtransform coefficients to coefficient quantization unit 506. Coefficientquantization unit 506 may be configured to perform quantization of thetransform coefficients. The quantization process may reduce the bitdepth associated with some or all of the coefficients. The degree ofquantization may alter the rate-distortion (i.e., bit-rate vs. qualityof video) of encoded video data. The degree of quantization may bemodified by adjusting a quantization parameter (QP). A quantizationparameter may be determined based on slice level values and/or CU levelvalues (e.g., CU delta QP values). QP data may include any data used todetermine a QP for quantizing a particular set of transformcoefficients. As illustrated in FIG. 5 , quantized transformcoefficients (which may be referred to as level values) are output toinverse quantization and transform coefficient processing unit 508.Inverse quantization and transform coefficient processing unit 508 maybe configured to apply an inverse quantization and an inversetransformation to generate reconstructed residual data. As illustratedin FIG. 5 , at summer 510, reconstructed residual data may be added to apredictive video block. In this manner, an encoded video block may bereconstructed and the resulting reconstructed video block may be used toevaluate the encoding quality for a given prediction, transformation,and/or quantization. Video encoder 500 may be configured to performmultiple coding passes (e.g., perform encoding while varying one or moreof a prediction, transformation parameters, and quantizationparameters). The rate-distortion of a bitstream or other systemparameters may be optimized based on evaluation of reconstructed videoblocks. Further, reconstructed video blocks may be stored and used asreference for predicting subsequent blocks.

Referring again to FIG. 5 , intra prediction processing unit 512 may beconfigured to select an intra prediction mode for a video block to becoded. Intra prediction processing unit 512 may be configured toevaluate a frame and determine an intra prediction mode to use to encodea current block. As described above, possible intra prediction modes mayinclude planar prediction modes, DC prediction modes, and angularprediction modes. Further, it should be noted that in some examples, aprediction mode for a chroma component may be inferred from a predictionmode for a luma prediction mode. Intra prediction processing unit 512may select an intra prediction mode after performing one or more codingpasses. Further, in one example, intra prediction processing unit 512may select a prediction mode based on a rate-distortion analysis. Asillustrated in FIG. 5 , intra prediction processing unit 512 outputsintra prediction data (e.g., syntax elements) to entropy encoding unit518 and transform coefficient generator 504. As described above, atransform performed on residual data may be mode dependent (e.g., asecondary transform matrix may be determined based on a predicationmode).

Referring again to FIG. 5 , inter prediction processing unit 514 may beconfigured to perform inter prediction coding for a current video block.Inter prediction processing unit 514 may be configured to receive sourcevideo blocks and calculate a motion vector for PUs of a video block. Amotion vector may indicate the displacement of a PU of a video blockwithin a current video frame relative to a predictive block within areference frame. Inter prediction coding may use one or more referencepictures. Further, motion prediction may be uni-predictive (use onemotion vector) or bi-predictive (use two motion vectors). Interprediction processing unit 514 may be configured to select a predictiveblock by calculating a pixel difference determined by, for example, sumof absolute difference (SAD), sum of square difference (SSD), or otherdifference metrics. As described above, a motion vector may bedetermined and specified according to motion vector prediction. Interprediction processing unit 514 may be configured to perform motionvector prediction, as described above. Inter prediction processing unit514 may be configured to generate a predictive block using the motionprediction data. For example, inter prediction processing unit 514 maylocate a predictive video block within a frame buffer (not shown in FIG.5 ). It should be noted that inter prediction processing unit 514 mayfurther be configured to apply one or more interpolation filters to areconstructed residual block to calculate sub-integer pixel values foruse in motion estimation. Inter prediction processing unit 514 mayoutput motion prediction data for a calculated motion vector to entropyencoding unit 518.

Referring again to FIG. 5 , filter unit 516 receives reconstructed videoblocks and coding parameters and outputs modified reconstructed videodata. Filter unit 516 may be configured to perform deblocking and/orSample Adaptive Offset (SAO) filtering. SAO filtering is a non-linearamplitude mapping that may be used to improve reconstruction by addingan offset to reconstructed video data. It should be noted that asillustrated in FIG. 5 , intra prediction processing unit 512 and interprediction processing unit 514 may receive modified reconstructed videoblock via filter unit 216. Entropy encoding unit 518 receives quantizedtransform coefficients and predictive syntax data (i.e., intraprediction data and motion prediction data). It should be noted that insome examples, coefficient quantization unit 506 may perform a scan of amatrix including quantized transform coefficients before thecoefficients are output to entropy encoding unit 518. In other examples,entropy encoding unit 518 may perform a scan. Entropy encoding unit 518may be configured to perform entropy encoding according to one or moreof the techniques described herein. In this manner, video encoder 500represents an example of a device configured to generate encoded videodata according to one or more techniques of this disclose.

Referring again to FIG. 1 , data encapsulator 107 may receive encodedvideo data and generate a compliant bitstream, e.g., a sequence of NALunits according to a defined data structure. A device receiving acompliant bitstream can reproduce video data therefrom. Further, asdescribed above, sub-bitstream extraction may refer to a process where adevice receiving a ITU-T H.265 compliant bitstream forms a new ITU-TH.265 compliant bitstream by discarding and/or modifying data in thereceived bitstream. It should be noted that the term conformingbitstream may be used in place of the term compliant bitstream. In oneexample, data encapsulator 107 may be configured to generate syntaxaccording to one or more techniques described herein. It should be notedthat data encapsulator 107 need not necessary be located in the samephysical device as video encoder 106. For example, functions describedas being performed by video encoder 106 and data encapsulator 107 may bedistributed among devices illustrated in FIG. 4 .

As described above, in one example, according to the techniques herein,reference picture lists may be signaled directly as follows: a set ofcandidate picture lists may be signaled in the SPS (or other parameterset, e.g., VPS) and one to three indices to the SPS candidate picturelists may be signaled in the slice segment header or new referencepicture lists may be signaled directly in slice segment header. A slicesegment header may is some cases be referred to as a segment header.Table 4 illustrates an example of relevant syntax that may be includedin an SPS and Table 5 illustrates an example of relevant syntax in the aslice segment header that may be used for directly signaling referencepicture lists according to the techniques herein. It should be notedthat syntax included in Table 4 is not limited to being included in anSPS (e.g., the syntax may be included in a parameter set) and syntaxincluded in Table 5 is not limited to being included in a slice segmentheader (e.g., the syntax may be included in a header associated withanother type of picture region, e.g., a picture header or a tile setheader).

TABLE 4 seq_parameter_set_rbsp( ) { Descriptor ... num_ref_pic_lists_minus1 ue(v)  for( i = 1; i <num_ref_pic_lists_minus1+1; i++)   pic_list( i )  rbsp_trailing_bits( )}

TABLE 5 slice_header( ) { Descriptor  ...    num_rpl_slice_header_minus1 u(2)    rpl_sps_flag u(1)    if(!rpl_sps_flag ) {     for( i = num_ref_pic_lists_minus1+1; i <num_ref_pic_lists_minus1+num_rpl_slice_header_ minus1+2; i++)     pic_list(i)    }    else {     for( j = 0; j < num_rpl_slice_headerminus1+1; j++)     rpl_index[j] u(v)    }  byte_alignment( ) }

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 4.

-   -   num_ref_pic_lists_minus1 specifies the number of pic_lists(i)        syntax structures included in the SPS. The value of        num_ref_pic_lists_minus1 shall be in the range of 0 to 255,        inclusive. pic_list(0) is inferred to be a null list of        pictures. Thus pic_list(0) does not include any pictures.    -   A decoder should allocate memory for a total number of        (num_ref_pic_lists_minus1+4) pic_list( ) syntax structures since        there may be up to 3 pic_list( ) syntax structure directly        signalled in the slice headers of a current picture.

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 5.

-   -   num_rpl_slice_header_minus1 specifies the number of pic_lists(i)        syntax structures signaled directly in the slice header if        rpl_sps_flag is equal to 0 or specifies the number of        rpl_index[j] entries signaled in the slice header if        rpl_sps_flag is equal to 1. The value of        num_rpl_slice_header_minus1 shall be in the range of 0 to 2,        inclusive. The value 3 is reserved.    -   rpl_sps_flag equal to 1 specifies that the reference picture        list(s) for the current picture are signaled based on pic_list(        ) syntax structures in the active SPS as identified by the        syntax element(s) rpl_idx[j] in the slice header. rpl_sps_flag        equal to 0 specifies that the the reference picture list(s) for        the current picture are signaled in the pic_list( ) syntax        structure(s) that are directly signaled in the slice headers of        the current picture.

rpl_idx[j] specifies the indices for reference picture list(s).rpl_idx[0] specifies an index for the reference picture list 0 for thecurrent picture. If present, rplidx[1] specifies an index for thereference picture list 1 if current slice is a B slice and specifies anindex for the list of pictures which include reference pictures forpictures following the current picture in the bitstream order, if thecurrent slice is a P slice. If present, rpl_idx[2] specifies an indexfor the list of pictures which include reference pictures for picturesfollowing the current picture in the bitstream order.

-   -   The syntax element rpl_idx[j] for j in the range of 0 to        num_rpl_slice_header_minus1 inclusive is represented by        Ceil(Log2(num_ref_pic_lists_minus1+1)) bits. The value of        rpl_idx[j] shall be in the range of 0 to        num_ref_pic_lists_minus1, inclusive.

Table 6 illustrates an example of pic_list syntax according to thetechniques herein.

TABLE 6 pic_list( listIdx ) { Descriptor  if(listIdx>2)   inv_list_flagu(1)  if(inv_list_flag==0) {   neg_delta_entries ue(v)   pos_delta_entries ue(v)   for( i = 0; i <neg_delta_entries+pos_delta_entries; i++ )    delta_entries_minus1[ i ]ue(v)  } }

Table 7 illustrates another example of pic_list syntax according to thetechniques herein.

TABLE 7 pic_list( listIdx) { Descriptor  if(listIdx>2)   inv_list_flagu(1)  if(inv_list_flag==0) {   neg_delta_entries ue(v)  pos_delta_entries ue(v)   for( i = 0; i < neg_delta_entries; i++ ) {   delta_entries_minus1[ i ] ue(v)   }   for( i = neg_delta_entries; i <  neg_delta_entries+pos_delta_entries; i++ ) {    delta_entries_minus1[i ] ue(v)   }  } }

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 6 and Table 7.

-   -   inv_list_flag equal to 1 specifies that the listIdx-th list of        pictures is derived from (listIdx-1)-th list of pictures by        inverting the sign of each delta POC value in the (listIdx-1)-th        list. inv_list_flag equal to 0 specifies that the listIdx-th        list of pictures is signaled. When inv_list_flag is not present,        it is inferred to be equal to 0.    -   neg_delta_entries specifies the number of entries in the        listIdx-th list of pictures that have picture order count values        less than the picture order count value of the current picture.        The value of neg_delta_entries shall be in the range of 0 to        sps_max_dec_pic_buffering_minus1 [sps_max_sub_layers_minus1],        inclusive.    -   pos_delta_entries specifies the number of entries in the        listIdx-th list of pictures that have picture order count values        greater than the picture order count value of the current        picture. The value of pos_delta_entries shall be in the range of        0 to sps_max_dec_pic_buffering_minus1        [sps_max_sub_layers_minus1]−neg_delta_entries, inclusive.

With respect to the example illustrated in Table 6, in one example, thefollowing definitions may be used for syntax elementdelta_entries_minus1.

delta_entries_minus1[i] plus 1,

-   -   when i is equal to 0, specifies the difference between the        picture order count values of the current picture and i-th entry        in the listIdx-th list of pictures that has picture order count        value less than that of the current picture, or,    -   when i is greater than 0 and less than neg_delta_entries,        specifies the difference between the picture order count values        of the i-th entry and the (i+1)-th entry in the listIdx-th list        of pictures that have picture order count values less than the        picture order count value of the current picture, or,    -   when i is equal to neg_delta_entries, specifies the difference        between the picture order count values of the current picture        and the i-th entry in the listIdx-th list of pictures that has        picture order count value greater than that of the current        picture, or,    -   when i is greater than neg_delta_entries, specifies the        difference between the picture order count values of the        (i+1)-th entry and i-th entry in the listIdx-th list of pictures        that have picture order count values greater than the picture        order count value of the current picture.

The value of delta_entries_minus1[i] shall be in the range of 0 to2¹⁵−1, inclusive.

When inv_list_flag is equal to 0, the variablesNumNegativePics[listIdx], NumPositivePics[listIdx],NumPositivePics[listIdx], DeltaPoc[listIdx][i] are derived as follows:

NumNegativePics[ listIdx ] = neg_delta_entries NumPositivePics[ listIdx] = pos_delta_entries NumDeltaPocs[ listIdx ] = NumNegativePics[ listIdx] + NumPositivePics[ listIdx ] - If i is equal to 0, the followingapplies:  DeltaPoc[ listIdx ][ i ] = −(delta_entries_minus1[ 0 ] + 1 ) -If i is > 0 and less than neg_delta_entries, the following applies: DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i − 1 ] −(delta_entries_minus1[ i ] + 1 ) - If i is equal to neg_delta_entries,the following applies:  DeltaPoc[ listIdx ][ neg_delta_entries ] =delta_entries_minus1[ i ] + 1 - If i is > neg_delta_entries, thefollowing applies:  DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i −1 ] +  (delta_entries_minus1[ i ] + 1)

When inv_list_flag is equal to 1, the variablesNumNegativePics[listIdx], NumPositivePics[listIdx],NumDeltaPocs[listIdx], DeltaPoc[listIdx][i] are derived as follows:

NumNegativePics[ listIdx ] = NumPositivePics[ listIdx-1 ]NumPositivePics[ listIdx ] = NumNegativePics[ listIdx-1 ] NumDeltaPocs[listIdx ] = NumDeltaPocs[ listIdx-1 ] - For i in the range of 0 toNumDeltaPocs[ listIdx ], inclusive the following applies:  DeltaPoc[listIdx ][ i ] = −(DeltaPoc[ listIdx-1 ][ i ] )

With respect to the example illustrated in Table 7, in one example, thefollowing definitions may be used for syntax elementdelta_entries_minus1.

delta_entries_minus1[i] plus 1,

-   -   when i is equal to 0, specifies the difference between the        picture order count values of the current picture and i-th entry        in the listIdx-th list of pictures that has picture order count        value less than that of the current picture, or,    -   when i is greater than 0 and less than neg_delta_entries,        specifies the difference between the picture order count values        of the i-th entry and the (i+1)-th entry in the listIdx-th list        of pictures that have picture order count values less than the        picture order count value of the current picture, or,    -   when i is equal to neg_delta_entries, specifies the difference        between the picture order count values of the current picture        and the i-th entry in the listIdx-th list of pictures that has        picture order count value greater than that of the current        picture, or,    -   when i is greater than neg_delta_entries, specifies the        difference between the picture order count values of the        (i+1)-th entry and i-th entry in the listIdx-th list of pictures        that have picture order count values greater than the picture        order count value of the current picture.

The value of delta_entries_minus1[i] shall be in the range of 0 to2¹⁵−1, inclusive.

When inv_list_flag is equal to 0, the variablesNumNegativePics[listIdx], NumPositivePics[listIdx],DeltaPocS0[listIdx][i], and DeltaPocS1[listIdx][i] are derived asfollows:

NumNegativePics[ listIdx ] = neg_delta_entries NumPositivePics[ listIdx] = pos_delta_entries - If i is equal to 0, the following applies: DeltaPocS0[ listIdx ][ i ] = −(neg_delta_entries_minus1[ i ] + 1 ) DeltaPocS1[ listIdx ][ i ] = pos_delta_entries_minus1[ i ] + 1 -Otherwise, the following applies:  DeltaPocS0[ listIdx ][ i ] =DeltaPocS0[ stRpsIdx ][ i − 1 ]  −(neg_delta_entries minus1[ i ] + 1 ) DeltaPocS1[ listIdx ][ i ] = DeltaPocS1[ stRpsIdx ][ i − 1 ] + (pos_delta_entries_minus1[ i ] + 1

The variable NumDeltaPocs[listIdx] is derived as follows:

 NumDeltaPocs[ listIdx ]   =   NumNegativePics[ listIdx ]   +NumPositivePics[ listIdx ]

Based on the syntax provided above in Tables 4-7, in one example, aprocess for deriving reference picture lists (RPL)s, i.e., a processperformed by a video decoder at the onset of decoding a picture may beperformed according to and/or based the following steps: The followingapplies:

The variable CurrRPListIdx[j] for j in the range of 0 tonum_rpl_slice_header_minus1, inclusive,is derived as follows: - Ifrpl_sps_flag is equal to 1, CurrRPListIdx[j] is set equal torpl_idx[j]. - Otherwise, CurrRPListIdx[j] is set equal torpl_idx[num_ref_pic_lists_minus1+j+1].

The following applies for j in the range of 0 tonum_rpl_slice_header_minus1, inclusive,

for( i = 0; i < NumDeltaPocs[ CurrRPListIdx[j] ]; i++ )  if( there is ashort-term reference picture picX in the DPB    with PicOrderCntValequal to (PicOrderCntVal + DeltaPoc[ CurrRPListIdx[j] ][ i ]) )  RefPics[ j ][ i ] = picX  else   RefPics[ j ][ i ] = ″no referencepicture″

All reference pictures in the DPB that are not included in RefPics[j]for j in the range of 0 to num_rpl_slice_header_minus1, inclusive, aremarked as “unused for reference”.

In one example, for the case where Otherwise, CurrRPListIdx[j] is setequal to rpl_idx[num_ref_pic_lists_minus1+j+1] the following may beperformed

for( i = 0; i < NumDeltaPocs[ CurrRPListIdx[j] ] ; i++ )   PocSt[ i ] =PicOrderCntVal + DeltaPoc[ CurrRPListIdx[j] ][ i ] for( i = 0; i <NumDeltaPocs[ CurrRPListIdx[j] ]; i++ )  if( there is a short-termreference picture picX in the DPB    with PicOrderCntVal equal to PocSt[ i ] )   RefPics[ j ][ i ] = picX  else   RefPics[ j ][ i ] = ″noreference picture″

Further, based on the syntax provided above in Tables 4-7, in oneexample, a process for reference picture lists construction, i.e., aprocess performed by a video decoder at the beginning of the decodingprocess for each P or B slice for constructing the reference picturelists RefPicList0 and, for B slices, RefPicList1 may be as performedbased on the following:

The variable NumRpsCurrList0 is set equal toMax(num_ref_idx_l0_active_minus1+1, NumDeltaPocs[CurrRPListIdx[0]]) andthe list RefPicList0 is constructed as follows:

for( i = 0, rIdx=0; i < NumDeltaPocs[ CurrRPListIdx[0] ] && rIdx <NumRpsCurrList0; rIdx++, i++ )  RefPicList0[ rIdx ] = RefPics[ 0 ][ i ]

When the slice is a B slice, the variable NumRpsCurrList1 is set equalto Max(num_ref_idx_l1_active_minus1+1, NumDeltaPocs[CurrRPListIdx[0]])and the list RefPicList1 is constructed as follows:

for( i = 0, rIdx=0; i < NumDeltaPocs[ CurrRPListIdx[1] ] && rIdx <NumRpsCurrList1; rIdx++, i++ )  RefPicList1[ rIdx ] = RefPics[ 1 ][ i ]

In another example, constructing the reference picture lists RefPicList0and, for B slices, RefPicList1 may be as performed based on thefollowing, where a RPL modification may be present:

The list RefPicList0 is constructed as follows.

The RefPicList0 entries above are assigned to RefPicListTemp0 andRefPicList1 entries above are assigned to RefPicListTemp1 arrayrespectively. Then final reference picture lists are derived as

for( rIdx = 0; rIdx <= num_ref_idx_l0_active_minus1; rIdx++) RefPicList0[ rIdx ] = ref_pic_list_modification_flag_l0 ?RefPicListTemp0[ list_entry_l0[ rIdx ] ] : RefPicListTemp0[ rIdx ]

When the slice is a B slice, the list RefPicList1 is constructed asfollows:

 for( rIdx = 0; rIdx <= num_ref_idx_l1_active_minus1; rIdx++)  RefPicList1[ rIdx ]  =  ref_pic_list_modification_flag_l1 ?RefPicListTemp1[ list_entry_l1[ rIdx ] ] :  RefPicListTemp1[ rIdx ]

Further, based on the syntax provided above in Tables 4-7, in oneexample, a process for generating unavailable reference pictures may beperformed according to and/or based the following steps:

This process is invoked once per coded picture.

When this process is invoked, the following applies:

-   -   For each RefPics[j][i], with i in the range of 0 to        NumDeltaPocs[CurrRPListIdx[j]], inclusive, for j in the range 0        to num_rpl_slice_header_minus1, inclusive, that is equal to “no        reference picture”, a picture is generated as specified in        “generation of one unavailable picture”, and the following        applies:        -   The value of PicOrderCntVal for the generated picture is set            equal to PicOrderCntVal+DeltaPoc[CurrRPListIdx[j]][i].        -   The generated picture is marked as “used for short-term            reference”.        -   RefPics[j][i], is set to be the generated reference picture.

Further, based on the syntax provided above in Tables 4-7, in oneexample, a process for generating one unavailable reference pictures maybe performed according to and/or based the following steps:

When this process is invoked, an unavailable picture is generated asfollows:

-   -   The value of each element in the sample array S_(L) for the        picture is set equal to 1<<(BitDepthy−1).    -   The value of each element in the sample arrays S_(Cb) and S_(Cr)        for the picture is set equal to 1<<(BitDepthc−1).    -   The prediction mode CuPredMode[x][y] is set equal to MODE_INTRA        for x=0 . . . pic_width_in_luma_samples−1, y=0 . . .        pic_height_in_luma_samples−1.

Further, based on the syntax provided above in Tables 4-7, in oneexample, a process for selecting a reference picture may be performedaccording to and/or based the following steps:

-   -   Input to this process is a reference index refIdxLX.    -   Output of this process is a reference picture consisting of a        two-dimensional array of luma samples refPicLX_(L) and two        two-dimensional arrays of chroma samples refPicLX_(Cb) and        refPicLX_(Cr).    -   The output reference picture RefPicListX[refIdxLX] consists of a        pic_width_in_luma_samples by pic_height_in_luma_samples array of        luma samples refPicLX_(L) and two PicWidthInSamplesC by        PicHeightlnSamplesC arrays of chroma samples refPicLX_(Cb) and        refPicLX_(Cr).    -   The reference picture sample arrays refPicLX_(L), refPicLX_(Cb),        and refPicLX_(Cr) correspond to decoded sample arrays S_(L),        S_(Cb), and S_(Cr) for a previously-decoded picture.

In one example, according to the techniques herein, long-term referencepicture lists may be signaled directly, as provided in further detailbelow. Table 8 illustrates an example of relevant syntax that may beincluded in an SPS for signaling long-term reference picture listsdirectly. It should be noted that syntax included in Table 8 is notlimited to being included in an SPS (e.g., the syntax may be included ina parameter set).

TABLE 8 seq_parameter_set_rbsp( ) { Descriptor ... long_term_refjpics_present_flag u(1)  num_ref_pic_lists_minus1 ue(v) for( i = 1; i < num_ref_pic_lists_minus1+1; i++)   pic_list( i ) rbsp_trailing_bits( ) }

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 8.

-   -   long_term_ref_pics_present_flag equal to 0 specifies that no        long-term reference picture is used for inter prediction of any        coded picture in the CVS. long_term_ref pics_present_flag equal        to 1 specifies that long-term reference pictures may be used for        inter prediction of one or more coded pictures in the CVS.    -   num_ref_pic_lists_minus1 specifies the number of pic_lists(i)        syntax structures included in the SPS. The value of        num_ref_pic_lists_minus1 shall be in the range of 0 to 255,        inclusive.    -   pic_list(0) is inferred to be a null list of pictures. Thus        pic_list(0) does not include any pictures.    -   A decoder should allocate memory for a total number of        (num_ref_pic_lists_minus1+4) pic_list( ) syntax structures since        there may be up to 3 pic_list( ) syntax structure directly        signalled in the slice headers of a current picture.

Table 9 illustrates an example of pic_list syntax that may be used inconjunction with the example syntax illustrated in Table 8.

TABLE 9 pic_list( listIdx ) { Descriptor  if(listIdx>2)   inv_list_flagu(1)   if(inv_list_flag===0) {   neg_delta_entries ue(v)  pos_delta_entries ue(v)   for( i = 0; i <neg_delta_entries+pos_delta_entries; i++ )    delta_entries_minus1[ i ]ue(v)  }  if(long_term_ref_pics_present_flag) {   ltrp_list_present_flag  if( ltrp_list_present_flag) {   num_long_term_pics_minus1 ue(v)   for(j = 0; j < num_long_term_pics_minus1+1; j++ ) {     poc_lsb_lt[ j ] u(v)    delta_poc_msb_present_flag[ j ] u(1)     if(delta_poc_msb_present_flag[ j ] )      delta_poc_msb_cycle_lt[ j ] ue(v)   }   }  } }

-   -   In one example, the following definitions may be used for the        respective syntax elements illustrated in Table 9.    -   inv_list_flag equal to 1 specifies that the listIdx-th list of        pictures is derived from (listIdx-1)-th list of pictures by        inverting the sign of each delta POC value in the (listIdx-1)-th        list. inv_list_flag equal to 0 specifies that the listIdx-th        list of pictures is signaled. When inv_list_flag is not present,        it is inferred to be equal to 0.    -   neg_delta entries specifies the number of entries in the        listIdx-th list of pictures that have picture order count values        less than the picture order count value of the current picture.        The value of neg_delta_entries shall be in the range of 0 to        sps_max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1],        inclusive.    -   pos_delta_entries specifies the number of entries in the        listIdx-th list of pictures that have picture order count values        greater than the picture order count value of the current        picture. The value of pos_delta_entries shall be in the range of        0 to sps_max_dec_pic_buffering_minus1        [sps_max_sub_layers_minus1]−neg_delta_entries, inclusive.    -   delta_entries_minus1[i] plus 1,        -   when i is equal to 0, specifies the difference between the            picture order count values of the current picture and i-th            entry in the listIdx-th list of pictures that has picture            order count value less than that of the current picture, or,        -   when i is greater than 0 and less than neg_delta_entries,            specifies the difference between the picture order count            values of the i-th entry and the (i+1)-th entry in the            listIdx-th list of pictures that have picture order count            values less than the picture order count value of the            current picture, or,        -   when i is equal to neg_delta_entries, specifies the            difference between the picture order count values of the            current picture and the i-th entry in the listIdx-th list of            pictures that has picture order count value greater than            that of the current picture, or,        -   when i is greater than neg_delta_entries, specifies the            difference between the picture order count values of the            (i+1)-th entry and i-th entry in the listIdx-th list of            pictures that have picture order count values greater than            the picture order count value of the current picture.    -   The value of delta_entries_minus1[i] shall be in the range of 0        to 2¹⁵−1, inclusive.    -   ltrp_list_present_flag equal to 0 specifies that no long-term        reference pictures are signaled in this picture list.        ltrp_list_present_flag equal to 1 specifies that long-term        reference pictures are signaled in this picture list and        num_long_term_pics_minus1, poc_lst_lt[j],        delta_poc_msb_present_flag[j] are present and        delta_po_msb_cycle_lt[j] may be present. When not present        ltrp_list_present_flag is inferred to be equal to 0.    -   num_long_term_pics_minus1 plus 1 specifies the number of        long-term reference picture entries in the picture list. The sum        of NumNegativePics[listIdx], NumPositivePics[listIdx],        (num_long_term_pics_minus1+1) shall be less than or equal to        sps_max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1].    -   poc_lsb_lt[j] specifies the value of the picture order count        modulo MaxPicOrderCntLsb of the j-th long-term reference picture        in the list. The length of the poc_lsb_lt[i] syntax element is        log2_max_pic_order_cnt_lsb_minus4+4 bits.    -   delta_poc_msb_present_flag[j] equal to 1 specifies that        delta_poc_msb_cycle_lt[j] is present.        delta_poc_msb_present_flag[j] equal to 0 specifies that        delta_poc_msb_cycle_lt[j] is not present.    -   delta_poc_msb_cycle_lt[j] is used to determine the value of the        most significant bits of the picture order count value of the        j-th long-term reference picture in the list. When        delta_poc_msb_cycle_lt[j] is not present, it is inferred to be        equal to 0. The variable DeltaPocMsbCycleLt[j] is derived as        follows:

if(j == 0 )  DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] else DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] +DeltaPocMsbCycleLt[ j − 1 ]

-   -   When inv_list_flag is equal to 0, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumPositivePics[listIdx], DeltaPoc[listIdx][i] are derived as        follows:

NumNegativePics[ listIdx ] = neg_delta_entries NumPositivePics[ listIdx] = pos_delta_entries NumDeltaPocs[ listIdx ] = NumNegativePics[ listIdx] + NumPositivePics[ listIdx ] - If i is equal to 0, the followingapplies:  DeltaPoc[ listIdx ][ i ] = −(delta_entries_minus1[ 0 ] + 1 ) -If i is > 0 and less than neg_delta_entries, the following applies: DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i − 1 ] −(delta_entries_minus1[ i ] + 1 ) - If i is equal to neg_delta_entries,the following applies:  DeltaPoc[ listIdx ][ neg_delta_entries ] =delta_entries_minus1[ i ] + 1 - If i is > neg_delta_entries, thefollowing applies:  DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i −1 ] +  (delta_entries_minus1[ i ] + 1)

-   -   When inv_list_flag is equal to 1, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumDeltaPocs[listIdx], DeltaPoc[listIdx][i] are derived as        follows:

NumNegativePics[ listIdx ] = NumPositivePics[ listIdx-1 ]NumPositivePics[ listIdx ] = NumNegativePics[ listIdx-1 ] NumDeltaPocs[listIdx ] = NumDeltaPocs[ listIdx-1 ]

-   -   -   For i in the range of 0 to NumDeltaPocs[listIdx], inclusive            the following applies:

  DeltaPoc[ listIdx ][ i ] = −( DeltaPoc[ listIdx-1 ][ i ] ) Ifltrp_list_present_flag is equal to 0 NumPocLt[ listIdx ] is set equal to0 Otherwise: NumPocLt[ listIdx ] = num_long_term_pics_minus1+1 for( j =0; j < num_long_term_pics_minus1+1; j++ ) {  DpocLt[ listIdx ][ j ] =poc_lsb_lt[ j ] − (delta_poc_msb_present_flag [ j ] ?DeltaPocMsbCycleLt[ j ]*MaxPicOrderCntLsb : 0)   DeltaPocMsbPresentFlag[listIdx ][ j ] = delta_poc_msb_present_   flag[ j ] }

-   -   Based on the syntax provided above in Table 8 and Table 9, in        one example, a process for deriving reference picture lists        (RPL)s may be performed according to and/or based the following        steps. The steps may be executed in sequence shown below or in a        different order:    -   The following applies:        -   The variable CurrRPListIdx[j] for j in the range of 0 to            num_rpl_slice_header_minus1, inclusive, is derived as            follows:

- If rpl_sps_flag is equal to 1, CurrRPListIdx[j] is set equal torpl_idx[j]  - Otherwise, CurrRPListIdx[j] is set equal torpl_idx[num_ref_pic_lists_minus1+j+1].

-   -   The following applies for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive,

for( i = 0; i < NumDeltaPocs[ CurrRPListIdx[j] ]; i++ )  if( there is ashort-term reference picture picX in the DPB    with PicOrderCntValequal to (PicOrderCntVal + DeltaPoc[ CurrRPListIdx[j] ][ i ]) )  RefPics[ j ][ i ] = picX  else  RefPics[ j ][ i ] = ″no referencepicture″

-   -   The following applies for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive:

for( m = 0; m< NumPocLt [CurrRPListIdx[j] ]; m++ )  if( !DeltaPocMsbPresentFlag[CurrRPListIdx[j] ][ m ] )   if( there is areference picture picX in the DPB with slice_pic_order_cnt_lsb equal toDPocLt[CurrRPListIdx[j] ] [ m ] )    RefPics[ j ][ NumDeltaPocs[CurrRPListIdx[j] ]+m ] = picX   else    RefPics[ j ][ NumDeltaPocs[CurrRPListIdx[j] ]+m ] = “no reference picture”  else   if( there is areference picture picX in the DPB with PicOrderCntVal equal to(DPocLt[CurrRPListIdx[j] ][ m ]-slice_pic_order_cnt_lsb+PicOrderCntVal))    RefPics[ j ] [ NumDeltaPocs[ CurrRPListIdx[j] ]+m ]= picX   else    RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ] =“no reference picture”

-   -   All reference pictures that are included in RefPics[j][k] for k        in the range NumDeltaPocs[CurrRPListIdx[j]] to        NumDeltaPocs[CurrRPListIdx[j]]+NumPocLt [CurrRPListIdx[j]]−1],        inclusive, for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, are marked as “used for        long-term reference”.    -   All reference pictures in the DPB that are not included in        RefPics[j] for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, are marked as “unused        for reference”.    -   Based on the syntax provided above in Table 8 and Table 9, in        one example, a process for generating unavailable pictures may        be performed according to and/or based the following steps:        -   For each RefPics[j][i], with i in the range of 0 to            NumDeltaPocs[CurrRPListIdx[j]], inclusive, for j in the            range 0 to num_rpl_slice_header_minus1, inclusive, that is            equal to “no reference picture”, a picture is generated as            specified in “generation of one unavailable picture”, and            the following applies:            -   The value of PicOrderCntVal for the generated picture is                set equal to                PicOrderCntVal+DeltaPoc[CurrRPListIdx[j]][i].            -   The generated picture is marked as “used for short-term                reference”.            -   RefPics[j][i], is set to be the generated reference                picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only        -   For each RefPics[j][i] for i in the range            NumDeltaPocs[CurrRPListIdx[j]] to            NumDeltaPocs[CurrRPListIdx[j]]+NumPocLt            [CurrRPListIdx[j]]−1], inclusive, for j in the range 0 to            num_rpl_slice_header_minus1, inclusive, that is equal to “no            reference picture”, a picture is generated as specified in            “generation of one unavailable picture”, and the following            applies:            -   The value of PicOrderCntVal for the generated picture is                set equal to                (DPocLt[CurrRPListIdx[j]][i-NumDeltaPocs[CurrRPListIdx[j]]-slice_pic_order_cnt_lsb+PicOrderCntVal)                if                DeltaPocMsbPresentFlag[CurrRPListIdx[j]][1-NumDeltaPocs[CurrRPListIdx[j]]                is equal to 1 Or is set equal to                DPocLaCurrRPListIdx[j]][NumDeltaPocs[CurrRPListIdx[j]]                otherwise (when                DeltaPocMsbPresentFlag[CurrRPListIdx[j]][i-NumDeltaPocs[CurrRPListIdx[j]]                is equal to 0)            -   The value of slicepic_order_cnt_lsb for the generated                picture is inferred to be equal to ((PicOrderCntVal for                the generated picture) & (MaxPicOrderCntLsb−1)).            -   The generated picture is marked as “used for long-term                reference”.            -   RefPics[j][i] is set to be the generated reference                picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only    -   Based on the syntax provided above in Table 8 and Table 9, in        one example, constructing the reference picture lists        RefPicList0 and, for B slices, RefPicList1 may be as performed        based on the following:    -   The variable NumRpsCurrList0 is set equal to        Max(num_ref_idx_l0_active_minus1+1,        NumDeltaPocs[CurrRPListIdx[0]]+NumPocLt[CurrRPListIdx[0]]) and        the list RefPicList0 is constructed as follows:

 for( i = 0, rIdx=0; i < (NumDeltaPocs[ CurrRPListIdx[0] ] ]+NumPocLt[CurrRPListIdx[0]]) && rIdx < NumRpsCurrList0; rIdx++, i++ )  RefPicList0[ rIdx ] = RefPics[ 0 ] [ i ] When the slice is a B slice,the variable NumRpsCurrList1 is set equal to Max(num_ref_idx_l1_active_minus1 + 1, NumDeltaPocs[CurrRPListIdx[0]]+NumPocLt[ CurrRPListIdx[1]]) ) and the listRefPicList1 is constructed as follows: for( i = 0, rIdx=0; i <(NumDeltaPocs[ CurrRPListIdx[1] ]+NumPocLt[ CurrRPListIdx[1]]) && rIdx <NumRpsCurrList1; rIdx++, i++ )   RefPicList1[ rIdx ] = RefPics[ l ][ i ]

Table 10 illustrates another example of relevant syntax that may beincluded in an SPS and Table 11 illustrates an example of relevantsyntax in slice segment header that may be used for signaling long-termreference picture lists directly according to the techniques herein. Itshould be noted that syntax included in Table 10 is not limited to beingincluded in an SPS and syntax included in Table 11 is not limited tobeing included in a slice segment header. In the example illustratedwith respect to Table 10 and Table 11, the long term reference picturerelated information is not included in the pic_list( ), but instead itis included in a separate long term ltrp_pic_list( ). It should be notedthat when the long term reference picture related information isincluded in a separate ltrp_pic_list( ), pic_list( ) may be based on theexample illustrated in Table 7.

TABLE 10 Descriptor seq_parameter_set_rbsp( ) {  ... long_term_ref_pics_present_flag u(1)  num_ref_pic_lists_minus1 ue(v) for( i = 1; i < num_ref_pic_lists_minus1+1; i++)   pic_list( i ) if(long_term_ref_pics_present_flag) {  num_ltrp_ref_pic_lists_minus1ue(v)  for( i = 0; i < num_ref_pic_lists_minus1+1; i++)   ltrp_pic_list(i )  }  rbsp_trailing_bits( ) }

TABLE 11 Descriptor slice_header( ) { ...    num_rpl_slice_header_minus1u(2)    rpl_sps_flag u(1)    if( !rpl_sps_flag ) {     for( i =num_ref_pic_lists_minus1+1; i <num_ref_pic_lists_minus1+num_rpl_slice_header_minus1+2; i++)    pic_list(i)    }    else {     for( j = 0; j <num_rpl_slice_header_minus1+1; j++)     rpl_idx[j] u(v)   }if(long_term_ref_pics_present_flag) {   num_ltrp_rpl_slice_header_minus1 u(2)    ltrp_rpl_sps_flag u(1)   if( !ltrp_rpl_sps_flag ) {     for( i =num_ltrp_ref_pic_lists_minus1+1; i <num_ltrp_ref_pic_lists_minus1+num_ltrp_rpl_slice_header_minus1+2; i++)    ltrp_pic_list(i)    }    else {     for( j = 0; j <num_ltrp_rpl_slice_header_minus1+1; j++)     ltrp_rpl_idx[j] u(v)    } } byte_alignment( ) }

-   -   In one example, the following definitions may be used for the        respective syntax elements illustrated in Table 10.    -   long_term_ref_pics_present_flag equal to 0 specifies that no        long-term reference picture is used for inter prediction of any        coded picture in the CVS.    -   long_term_ref_pics_present_flag equal to 1 specifies that        long-term reference pictures may be used for inter prediction of        one or more coded pictures in the CVS.    -   num_ref_pic_lists_minus1 specifies the number of pic_lists(i)        syntax structures included in the SPS. The value of        num_ref_pic_lists_minus1 shall be in the range of 0 to 255,        inclusive.    -   pic_list(0) is inferred to be a null list of pictures. Thus        pic_list(0) does not include any pictures.    -   A decoder should allocate memory for a total number of        (num_ref_pic_lists_minus1+4) pic_list( ) syntax structures since        there may be up to 3 pic_list( ) syntax structure directly        signalled in the slice headers of a current picture.    -   num_ltrp_ref_pic_lists_minus1 specifies the number of        ltrp_pic_lists(i) syntax structures included in the SPS. The        value of num_ltrp_ref_pic_lists_minus1 shall be in the range of        0 to 255, inclusive. A decoder should allocate memory for a        total number of (num_ltrp_ref_pic_lists_minus1+3) ltrp_pic_list(        ) syntax structures since there may be upto 2 ltrp_pic_list( )        syntax structure directly signalled in the slice headers of a        current picture.    -   In one example, the following definitions may be used for the        respective syntax elements illustrated in Table 11.    -   num_rpl_slice_header_minus1 specifies the number of pic_lists(i)        syntax structures signaled directly in the slice header if        rpl_sps_flag is equal to 0 or specifies the number of        rpl_index[j] entries signaled in the slice header if        rpl_sps_flag is equal to 1. The value of        num_rpl_slice_header_minus1 shall be in the range of 0 to 2,        inclusive. The value 3 is reserved.    -   rpl_sps_flag equal to 1 specifies that the reference picture        list(s) for the current picture are signaled based on pic_list(        ) syntax structures in the active SPS as identified by the        syntax element(s) rpl_idx[j] in the slice header. rpl_sps_flag        equal to 0 specifies that the the reference picture list(s) for        the current picture are signaled in the pic_list( ) syntax        structure(s) that are directly signaled in the slice headers of        the current picture.    -   rpl_idx[j] specifies the indices for reference picture list(s).        rpl_idx[0] specifies an index for the reference picture list 0        for the current picture. If present, rpl_idx[1] specifies an        index for the reference picture list 1 if current slice is a B        slice and specifies an index for the list of pictures which        include reference pictures for pictures following the current        picture in the bitstream order, if the current slice is a P        slice. If present, rpl_idx[2] specifies an index for the list of        pictures which include reference pictures for pictures following        the current picture in the bitstream order.    -   The syntax element rpl_idx[j] for j in the range of 0 to        num_rpl_slice_header_minus1 inclusive is represented by        Ceil(Log2(num_ref_pic_lists_minus1+1)) bits. The value of        rpl_idx[j] shall be in the range of 0 to        numref_pic_lists_minus1, inclusive.    -   num_ltrp_rpl_slice_header_minus1 specifies the number of        ltrp_pic_lists(i) syntax structures signaled directly in the        slice header if ltrp_rpl_sps_flag is equal to 0 or specifies the        number of ltrp_rpl_index[j] entries signaled in the slice header        if ltrp_rpl_sps_flag is equal to 1. The value of        num_ltrp_rpl_slice_header_minus1 shall be in the range of 0 to        1, inclusive. The value 2 and 3 are reserved.    -   In another example, only 1 bit (i.e. u(1)) may be used for        num_ltrp_rpl_slice_header_minus1 and its semantics will be as        follows:    -   num_ltrp_rpl_slice_header_minus1 specifies the number of        ltrp_pic lists(i) syntax structures signaled directly in the        slice header if ltrp_rpl_sps_flag is equal to 0 or specifies the        number of ltrp_rpl_index[j] entries signaled in the slice header        if ltrp_rpl_sps_flag is equal to 1.    -   ltrp_rpl_sps_flag equal to 1 specifies that the long-term        reference picture list(s) for the current picture are signaled        based on ltrp_pic_list( ) syntax structures in the active SPS as        identified by the syntax element(s) ltrp_rpl_idx[j] in the        slice_header. ltrp_rpl_sps_flag equal to 0 specifies that the        long-term reference picture list(s) for the current picture are        signaled in the ltrp_pic_list( ) syntax structure(s) that are        directly signaled in the slice headers of the current picture.    -   ltrp_rpl_idx[j] specifies the indices for long-term reference        picture list(s). ltrp_rpl_idx[0] specifies an index for use in        the construction of long-term reference picture list 0 and 1 for        the current picture. If present, rpl_idx[1] specifies an index        for the list of pictures which include long-term reference        pictures for pictures following the current picture in the        bitstream order.    -   The syntax element ltrp_rpl_idx[j] for j in the range of 0 to        num_ltrp_rpl_slice_header_minus1 inclusive is represented by        Ceil(Log2(num_ltrp_ref_pic_lists_minus1+1)) bits. The value of        ltrp_rpl_idx[j] shall be in the range of 0 to        num_ltrp_ref_pic_lists_minus1, inclusive.

Table 12 illustrates another example of ltrp_pic_list syntax that may beused in conjunction with the example syntax illustrated in Table 10 andTable 11.

TABLE 12 Descriptor ltrp_pic_list( ltrpListIdx ) { num_long_term_pics_minus1 ue(v)   for( j = 0; j <num_long_term_pics_minus1+1; j++ ) {   poc_lsb_lt[ j ] u(v)  delta_poc_msb_present_flag[ j ] u(1)   if( delta_poc_msb_present_flag[j ] )    delta_poc_msb_cycle_lt[ j ] ue(v)   } }

-   -   In one example, the following definitions may be used for the        respective syntax elements illustrated in Table 12.    -   num_long_term_pics_minus1 plus 1 specifies the number of        long-term reference picture entries in the picture list. The sum        of NumNegativePics[listIdx], NumPositivePics[listIdx],        (num_long_term_pics_minus1+1) shall be less than or equal to        sps_max_dec_pic_buffering_minus1[sps_max_sub_layers_minus1].    -   poc_lsb_lt[j] specifies the value of the picture order count        modulo MaxPicOrderCntLsb of the j-th long-term reference picture        in the list. The length of the poc_lsb_lt[i] syntax element is        log2_max_pic_order_cnt_lsb_minus4+4 bits.    -   delta_poc_msb_present_flag[i] equal to 1 specifies that        delta_poc_msb_cycle_lt[j] is present.        delta_poc_msb_present_flag[j] equal to 0 specifies that        delta_poc_msb_cycle_la j is not present.    -   delta_poc_msb_cycle_lt[i] is used to determine the value of the        most significant bits of the picture order count value of the        j-th long-term reference picture in the list. When        delta_poc_msb_cycle_lt[j] is not present, it is inferred to be        equal to 0. The variable DeltaPocMsbCycleLt[j] is derived as        follows:

if( j == 0 )  DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] else DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] +DeltaPocMsbCycleLt[ j − 1 ]

-   -   When inv_list_flag is equal to 0, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumPositivePics[listIdx], DeltaPoc[listIdx][i are derived as        follows:

NumNegativePics[ listIdx ] = neg_delta_entries NumPositivePics[ listIdx] = pos_delta_entries NumDeltaPocs[ listIdx ] = NumNegativePics[ listIdx] + NumPositivePics[ listIdx ]  If i is equal to 0, the followingapplies:   DeltaPoc[ listIdx ][ i ] = −(delta_entries_minus1[ 0 ] + 1 ) If i is > 0 and less than neg_delta_entries, the following applies:  DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i − 1 ]  −(delta_entries_minus1[ i ] + 1 )  If i is equal to neg_delta_entries,the following applies:   DeltaPoc[ listIdx ][ neg_delta_entries ] =delta_entries_minus1[ i ] + 1  If i is > neg_delta_entries, thefollowing applies:   DeltaPoc[ listIdx ][ i ] = DeltaPoc[ listIdx ][ i −1 ] +    (delta_entries_minus1[ i ] + 1 )

-   -   When inv_list_flag is equal to 1, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumDeltaPocs[listIdx], DeltaPod listIdx][i] are derived as        follows:

 NumNegativePics[ listIdx ] = NumPositivePics[ listIdx-1 ] NumPositivePics[ listIdx ] = NumNegativePics[ listIdx-1 ] NumDeltaPocs[ listIdx ] = NumDeltaPocs[ listIdx-1 ]   For i in therange of 0 to NumDeltaPocs[ listIdx ], inclusive the following  applies:    DeltaPoc[ listIdx ][ i ] = −(DeltaPoc[ listIdx-1 ][ i ] )If long_term_ref_pics_present_flag is equal to 0 then NumPocLt[ltrpListIdx ] is set equal to 0 Otherwise: NumPocLt[ ltrpListIdx ] =num_long_term_pics_minus1+1 for( j = 0; j < num_long_term_pics_minus1+1;j++ ) {   DpocLt[ ltrpListIdx ][ j ] = poc_lsb_lt[ j ] -(delta_poc_msb_present_flag[ j ] ? DeltaPocMsbCycleLt[ j]*MaxPicOrderCntLsb : 0)    DeltaPocMsbPresentFlag[ ltrpListIdx ][ j ] =delta_poc_msb_present_flag[ j ] }

-   -   Based on the syntax provided above in Table 10, Table 11 and        Table 12, in one example, a process for deriving reference        picture lists (RPL)s may be performed according to and/or based        the following steps. The steps may be executed in sequence shown        below or in a different order.    -   The following applies:        -   The variable CurrRPListIdx[j] for j in the range of 0 to            num_rpl_slice_header_minus1, inclusive, is derived as            follows:

 If rpl_sps_flag is equal to 1, CurrRPListIdx[j] is set equal torpl_idx[j]   Otherwise, CurrRPListIdx[j] is set equal torpl_idx[num_ref_pic_lists_minus1+j+1].

-   -   The following applies for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive,

for( i = 0; i < NumDeltaPocs[ CurrRPListIdx[j] ]; i++ )  if( there is ashort-term reference picture picX in the DPB    with PicOrderCntValequal to (PicOrderCntVal + DeltaPoc[ CurrRPListIdx[j] ][ i ]) )  RefPics[ j ][ i ] = picX  else   RefPics[ j ][ i ] = “no referencepicture”

-   -   The following applies for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, for n in the range of 0        to num_ltrp_rpl_slice_header_minus1, inclusive.:        -   The variable CurrLTRPRPListIdx[n] for n in the range of 0 to            num_ltrp_rpl_slice_header_minus1, inclusive, is derived as            follows:

 If ltrp_rpl_sps_flag is equal to 1, CurrLTRPRPListIdx[n] is set equalto ltrp_rpl_idx[n].   Otherwise, CurrLTRPRPListIdx[n] is set equal toltrp_rpl_idx[num_ltrp_ref_pic_lists_minus1+n+1]. for( m = 0; m< NumPocLt[CurrLTRPRPListIdx[n] ]; m++ )  if(!DeltaPocMsbPresentFlag[CurrLTRPRPListIdx[n] ][ m ] )   if( there is areference picture picX in the DPB with slice_pic_order_ent_lsb equal toDPocLt[CurrLTRPRPListIdx[n] ][ m ] )    RefPics[ j ][ NumDeltaPocs[CurrRPListIdx[j] ]+m ] = picX   else    RefPics[ j ][ NumDeltaPocs[CurrRPListIdx[j] ]+m ] = “no reference picture”  else   if( there is areference picture picX in the DPB with PicOrderCntVal equal to(DPocLt[CurrLTRPRPListIdx [n] ][ m ]-slice_pic_order_cnt_lsb+PicOrderCntVal))    RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ] =picX   else    RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ]= “noreference picture”

-   -   In another example the above steps:        -   only apply for j in the range of 0 to 1 if current slice is            a B slice or for j in the range of 0 if current slice is a P            slice for n equal to 0, and        -   only apply for j equal to max(2,            num_rpl_slice_header_minus1) if current slice is a B slice            or for j equal to max(1, num_rpl_slice_header_minus1) if            current slice is a P slice for n equal to max(1,            numitrp_rpl_slice_header_minus1), and    -   All reference pictures that are included in RefPics[j][k] for k        in the range NumDeltaPocs[CurrRPListidx[j]] to        NumDeltaPocs[CurrRPListIdx[j]]+NumPocLt        [CurrLTRPRPListIdx[n]]−1], inclusive, for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, are marked as “used for        long-term reference”.    -   All reference pictures in the DPB that are not included in        RefPics[j] for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, are marked as “unused        for reference”.    -   Based on the syntax provided above in Table 10, Table 11 and        Table 12, in one example, a process for generating unavailable        pictures may be performed according to and/or based the        following steps:    -   For each RefPics[j] [i], with i in the range of 0 to        NumDeltaPocs[CurrRPListIdx[j]], inclusive, for j in the range 0        to num_rpl_slice_header_minus1, inclusive, that is equal to “no        reference picture”, a picture is generated as specified in        “generation of one unavailable picture”, and the following        applies:    -   The value of PicOrderCntVal for the generated picture is set        equal to PicOrderCntVal+DeltaPoc[CurrRPListIdx[j]][i].    -   The generated picture is marked as “used for short-term        reference”.    -   RefPics[j][i], is set to be the generated reference picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only.    -   For each RefPics[j][i] for i in the range        NumDeltaPocs[CurrRPListIdx[j]] to        NumDeltaPocs[CurrRPListIdx[j]]+NumPocLt        [CurrLTRPRPListIdx[n]]−1], inclusive, for j in the range 0 to        num_rpl_slice_header_minus1, inclusive, n in the range of 0 to        num_ltrp_rpl_slice_header_minus1, that is equal to “no reference        picture”, a picture is generated as specified in “generation of        one unavailable picture”, and the following applies:        -   The value of PicOrderCntVal for the generated picture is set            equal to            (DPocLt[CurrLTRPRPListIdx[n]]]i-NumDeltaPocs[CurrRPListIdx[j]]-slicepic_order_cnt_lsb+PicOrderCntVal)            if            DeltaPocMsbPresentFlag[CurrLTRPRPListIdx[n]][i-NumDeltaPocs[CurrRPListIdx[j]]]            is equal to 1 Or is set equal to            DPocLt[CurrLTRPRPListIdx[n]][NumDeltaPocs[CurrRPListIdx[j]]]            otherwise (when            DeltaPocMsbPresentFlag[CurrLTRPRPListIdx[n]][i-NumDeltaPocs[CurrRPListIdx[j]]            ] is equal to 0).        -   The value of slice_pic_order_cnt_lsb for the generated            picture is inferred to be equal to ((PicOrderCntVal for the            generated picture) & (MaxPicOrderCntLsb−1)).        -   The generated picture is marked as “used for long-term            reference”.        -   RefPics[j][i] is set to be the generated reference picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only and for n equal to        num_ltrp_xpl_slice_header_minus1.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only.

Based on the syntax provided above in in Table 10, Table 11 and Table12, in one example, constructing the reference picture lists RefPicList0and, for B slices, RefPicList1 may be as performed based on thefollowing:

-   -   The variable NumRpsCurrList0 is set equal to        Max(num_ref_idx_l0_active_minus1+1,        NumDeltaPocs[CurrRPListIdx[0]]+NumPocLt[CurrLTRPRPListIdx[0]])        and the list RefPicList0 is constructed as follows:

 for( i = 0, rIdx=0; i < (NumDeltaPocs[ CurrRPListIdx[0] ] ]+NumPocLt[CurrRPListIdx[0]]) && rIdx < NumRpsCurrList0; rIdx++, i++ )  RefPicList0[ rIdx ] = RefPics[ 0 ][ i ]

-   -   When the slice is a B slice, the variable NumRpsCurrList1 is set        equal to Max(num_ref_idx_l1_active_minus1+1,        NumDeltaPocs[CurrRPListIdx[0]]+NumPocLt[CurrLTRPRPListIdx[0]]))        and the list RefPicList1 is constructed as follows:

for( i = 0, rIdx=0; i < (NumDeltaPocs[ CurrRPListIdx[1] ]+NumPocLt[CurrLTRPRPListIdx[0]]) && rIdx < NumRpsCurrList1 ; rIdx++, i++ ) RefPicList1 [ rIdx ] = RefPics[ 1 ][ i ]

In one example, a long-term reference picture list may be directlysignaled in a slice header. With respect to the example of SPS syntaxillustrated in Table 8, Table 13 illustrates an example of relevantsyntax in slice segment header that may be used for signaling long-termreference picture lists directly according to the techniques herein.Further, Table 14 provides an example of a long-term reference picturethat may be included in a slice segment header. It should be noted thatthe example long-term reference picture list illustrated in Table 14 isarranged such that first few entries (indicated by a syntax element orvariable) in the list signal Long-term reference picture (LTRP)information for the current picture and the remaining entries in thelist signal LTRP information for pictures following the current picturein the bitstream order.

TABLE 13 Descriptor slice_header( ) { ...    num_rpl_slice_header_minus1u(2)    rpl_sps_flag u(1)    if( !rpl_sps_flag ) {    for( i =num_ref_pic_lists_minus1+1; i <num_ref_pic_lists_minus1+num_rpl_slice_header_minus1+2; i++)    pic_list(i)    }    else {    for( j = 0; j <num_rpl_slice_header_minus1+1; j++)     rpl_idx[j] u(v)   }if(long_term_ref_pics_present_flag) {    ltrp_sl_list( ) } byte_alignment( ) }

TABLE 14 Descriptor ltrp_sl_list( ) {  num_long_term_pics_minus1 ue(v) num_currpic_long_term_pics ue(v)   for( j = 0; j <num_long_term_pics_minus1+1; j++ ) {   poc_lsb_lt[ j ] u(v)  delta_poc_msb_present_flag[ j ] u(1)   if( delta_poc_msb_present_flag[j ] )    delta_poc_msb_cycle_lt[ j ] ue(v)   } }

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 13.

-   -   num_rpl_slice_header_minus1 specifies the number of pic_lists(i)        syntax structures signaled directly in the slice header if        rpl_sps_flag is equal to 0 or specifies the number of        rpl_index[j] entries signaled in the slice header if        rpl_sps_flag is equal to 1. The value of        num_rpl_slice_header_minus1 shall be in the range of 0 to 2,        inclusive. The value 3 is reserved.    -   rpl_sps_flag equal to 1 specifies that the reference picture        list(s) for the current picture are signaled based on pic_list(        ) syntax structures in the active SPS as identified by the        syntax element(s) rpl_idx[j] in the slice_header. rpl_sps_flag        equal to 0 specifies that the the reference picture list(s) for        the current picture are signaled in the pic_listO syntax        structure(s) that are directly signaled in the slice headers of        the current picture.    -   rpl_idx[j] specifies the indices for reference picture list(s).        rpl_idx[0] specifies an index for the reference picture list 0        for the current picture. If present, rpl_idx[1] specifies an        index for the reference picture list 1 if current slice is a B        slice and specifies an index for the list of pictures which        include reference pictures for pictures following the current        picture in the bitstream order, if the current slice is a P        slice. If present, rpl_idx[2] specifies an index for the list of        pictures which include reference pictures for pictures following        the current picture in the bitstream order.    -   The syntax element rpl_idx[j] for j in the range of 0 to        num_rpl_slice_header_minus1 inclusive is represented by        Ceil(Log2(num_ref_pic_lists_minus1+1)) bits. The value of        rpl_idx[j] shall be in the range of 0 to        num_ref_pic_lists_minus1, inclusive.

In one example, the following definitions may be used for the respectivesyntax elements illustrated in Table 14.

-   -   num_long_term_pics_minus1 plus 1 specifies the number of        long-term reference picture entries in this ltrp_sl_list( )        list. This includes information for long-term reference picture        for the current picture and for pictures following the current        picture in the bitstream order.    -   num_currpic_long_term_pics specifies the number of long-term        reference picture entries in in this ltrp_sl_list( ) list for        the current picture.    -   Thus in the for loop in ltrp_sl_list( ), first        num_currpic_long_term_pics entries correspond to long-term        reference picture information for the current picture and        subsequent entries correspond to long-term reference picture        information for pictures following the current picture in the        bitstream order.    -   The sum of NumNegativePics[listIdx], NumPositivePics[listIdx],        (num_long_term_pics_minus1+1) shall be less than or equal to        sps_max_dec pic_buffering_minus1[sps_max_sub_layers_minus1].    -   poc_lsb_lt[j] specifies the value of the picture order count        modulo MaxPicOrderCntLsb of the j-th long-term reference        picture. The length of the poc_lsb_lt[i] syntax element is        log2_max_pic_order_cnt_lsb_minus4+4 bits.    -   delta_poc_msb_present_flag[j] equal to 1 specifies that        delta_poc_msb_cycle_lt[j] is present. delta_poc_msb        present_flag[j] equal to 0 specifies that        delta_poc_msb_cycle_lt[j] is not present.    -   delta_poc_msb_cyde_lt[j] is used to determine the value of the        most significant bits of the picture order count value of the        j-th long-term reference picture. When delta_poc_msb_cycle_lt[j]        is not present, it is inferred to be equal to 0. The variable        DeltaPocMsbCycleLt[j] is derived as follows:

if( j == 0 )  DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] else DeltaPocMsbCycleLt[ j ] = delta_poc_msb_cycle_lt[ j ] +DeltaPocMsbCycleLt[ j − 1 ]

-   -   When inv_list_flag is equal to 0, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumPositivePics[listIdx], DeltaPoc[listIdx][i] are derived as        follows:

NumNegativePics[ listIdx ] = neg_delta_entries NumPositivePics[ listIdx] = pos_delta_entries NumDeltaPocs[ listIdx ] = NumNegativePics[ listIdx] + NumPositivePics[ listIdx ]

-   -   -   If i is equal to 0, the following applies:            -   DeltaPoc[listIdx][i]=−(deltaentriesminus1[0]+1)        -   If i is >0 and less than neg_delta_entries, the following            applies:            -   DeltaPoc[listIdx][i]=DeltaPoc[listIdx][i−1]−(delta_entries_minus1[i]+1)        -   If i is equal to neg_delta_entries, the following applies:            -   DeltaPoc[listIdx][neg_delta_entries]=delta_entries_minus1[i]+1        -   If i is >neg_delta_entries, the following applies:            -   DeltaPoc[listIdx][i]=DeltaPoc[listIdx][i]−1+(delta_entries_minus1[i]+1)

    -   When inv_list_flag is equal to 1, the variables        NumNegativePics[listIdx], NumPositivePics[listIdx],        NumDeltaPocs[listIdx], DeltaPoc[listIdx][i] are derived as        follows:

NumNegativePics[ listIdx ] = NumPositivePics[ listIdx-1 ]NumPositivePics[ listIdx ] = NumNegativePics[ listIdx-1 ] NumDeltaPocs[listIdx ] = NumDeltaPocs[ listIdx-1 ]

-   -   -   For i in the range of 0 to NumDeltaPocs[listIdx], inclusive            the following applies:

DeltaPoc[ listIdx ][ i ] = −(DeltaPoc[ listIdx-1 ][ i ] ) Iflong_term_ref_pics_present_flag is equal to 0 NumPocLt is set equal to 0Otherwise: : NumPocLt = num_long_term_pics_minus1+1; NumPocLtCurr =num_currpic_long_term_pics; NumPocLtFoll=num_long_term_pics_minus1+1 -NumPocLtCurr; for( j = 0; j < num_long_term_pics_minus1+1; j++ ) { DpocLt[j] = poc_lsb_lt[ j ] - (delta_poc_msb_present_flag[ j ] ?DeltaPocMsbCycleLt[ j ]*MaxPicOrderCntLsb : 0)  DeltaPocMsbPresentFlag[j ] = delta_poc_msb_prcsent flag[ j ] }

-   -   Based on the syntax provided above in Table 13 and Table 14, in        one example, a process for deriving reference picture lists        (RPL)s may be performed according to and/or based the following        steps. The steps may be executed in sequence shown below or in a        different order.    -   The following applies:        -   The variable CurrRPListIdx[j] for j in the range of 0 to            num_rpl_slice_header_minus1, inclusive, is derived as            follows:

- If rpl_sps_flag is equal to 1, CurrRPListIdx[j] is set equal torpl_idx[j]  - Otherwise, CurrRPListIdx[j] is set equal torpl_idx[num_ref_pic_lists_minus1+j+1].

-   -   The following applies for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive,

for( i = 0; i < NumDeltaPocs[ CurrRPListIdx[j] ]; i++ )  if( there is ashort-term reference picture picX in the DPB    with PicOrderCntValequal to (PicOrderCntVal + DeltaPoc[ CurrRPListIdx[j] ][ i ]) )  RefPics[ j ][ i ] = picX  else   RefPics[ j ][ i ] = “no referencepicture”

-   -   for j in the range of in the range of 0 to 1 if current slice is        a B slice or for j in the range of 0 if current slice is a P        slice:

  for( m = 0; m< NumPocLtCurr; m++ )    if( ! DeltaPocMsbPresentFlag[ m] )       if(  there  is  a  reference  picture  picX  in  the  DPB with   slice_pic_order_cnt_lsb equal to DPocLt[ m ] )          RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ]  = picX      else           RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ] =  “no   reference picture”    else       if( there is a referencepicture picX in the DPB with PicOrderCntVal   equal to (DPocLt [ m]-slice_pic_order_cnt_lsb+ PicOrderCntVal))           RefPics[ j ][NumDeltaPocs[ CurrRPListIdx[j] ]+m ]  = picX       else          RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m ]   = “no  reference picture” And for j equal to max(2,num_rpl_slice_header_minus1) if current slice is a B slice or for jequal to max(1, num_rpl_slice_header_minus1)  if current slice is a Pslice  :   for( m = NumPocLtCurrs; m< NumPocLt; m++ )    if( !DeltaPocMsbPresentFlag[ m ] )       if( there is a reference picturepicX in the DPB with   slice_pic_order_cnt_lsb equal to DPocLt[ m ] )   RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m-NumPocLtCurr ]  =picX       else    RefPics[j ][ NumDeltaPocs[ CurrRPListIdx[j]]+m-NumPocLtCurr ]   = “no   reference picture”    else       if( thereis a reference picture picX in the DPB with PicOrderCntVal   equal to(DPocLt [ m ]-slice_pic_order_cnt_lsb+ PicOrderCntVal))    RefPics[ j ][NumDeltaPocs[ CurrRPListIdx[j] ]+m-NumPocLtCurr ]  = picX       else   RefPics[ j ][ NumDeltaPocs[ CurrRPListIdx[j] ]+m-NumPocLtCurr ]   = “no   reference picture” All  reference  pictures  that  are  included in  RefPics[ j ][ k ]  for  k  in  the  range NumDeltaPocs[CurrRPListIdx[j] ]    to    NumDeltaPocs[ CurrRPListIdx[j] ]+NumPocLtCurr−1], inclusive, for j in the range of in the range of 0 to 1if current slice is a B slice or for j in the range of 0 if currentslice is a P slice      and  for  k  in  the  range  NumDeltaPocs[CurrRPListIdx[j] ]  to   NumDeltaPocs[ CurrRPListIdx[j] ]+ NumPocLt−NumPocLtCurr−1], inclusive,   for j equal to max(2,num_rpl_slice_header_minus1) if current slice is a B slice or   for jequal to max(1, num_rpl_slice_header_minus1) if current slice is a Pslice      are marked as “used for long-term reference”.

-   -   All reference pictures in the DPB that are not included in        RefPics[j] for j in the range of 0 to        num_rpl_slice_header_minus1, inclusive, are marked as “unused        for reference”.    -   Based on the syntax provided above in Table 13 and Table 14, in        one example, a process for generating unavailable pictures may        be performed according to and/or based the following steps:    -   For each RefPics[j][i], with i in the range of 0 to        NumDeltaPocs[CurrRPListIdx[j]], inclusive, for j in the range 0        to num_rpl_slice_header_minus1, inclusive, that is equal to “no        reference picture”, a picture is generated as specified in        “generation of one unavailable picture”, and the following        applies:    -   The value of PicOrderCntVal for the generated picture is set        equal to PicOrderCntVal+DeltaPoc[CurrRPListIdx[j]][i].    -   The generated picture is marked as “used for short-term        reference”.    -   RefPics[j][i], is set to be the generated reference picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only    -   For each RefPics[j][i] for i in the range        NumDeltaPocs[CurrRPListIdx[j]] to        NumDeltaPocs[CurrRPListIdx[j]]+NumPocLtCurr]−1], inclusive, for        j in the range of in the range of 0 to 1 if current slice is a B        slice or for j in the range of 0 if current slice is a P slice,        that is equal to “no reference picture”, a picture is generated        as specified in “generation of one unavailable picture”, and the        following applies:        -   The value of PicOrderCntVal for the generated picture is set            equal to            (DPocLt[i-NumDeltaPocs[CurrRPListIdx[j]]-slice_pic_order_cnt_lsb+PicOrderCntVal)            if DeltaPocMsbPresentFlag [i-NumDeltaPocs[CurrRPListIdx[j]]            is equal to 1 Or is set equal to            DPocLt[i-NumDeltaPocs[CurrRPListIdx[j] otherwise (when            DeltaPocMsbPresentFlag [NumDeltaPocs[CurrRPListIdx[j]] is            equal to 0).        -   The value of slice_pic_order_cnt_lsb for the generated            picture is inferred to be equal to ((PicOrderCntVal for the            generated picture) & (MaxPicOrderCntLsb−1)).        -   The generated picture is marked as “used for long-term            reference”.        -   RefPics[j][i] is set to be the generated reference picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only.    -   For each RefPics[j][i] for i in the range        NumDeltaPocs[CurrRPListIdx[j]] to        NumDeltaPocs[CurrRPListIdx[j]]+NumPocLt-NumPocLtCurr]−1],        inclusive, for equal to max(2, num_rpl_slice_header_minus1) if        current slice is a B slice or for j equal to max(1,        num_rpl_slice_header_minus1) if current slice is a P slice, that        is equal to “no reference picture”, a picture is generated as        specified in “generation of one unavailable picture”, and the        following applies:        -   The value of PicOrderCntVal for the generated picture is set            equal to            (DPocLt[i-NumDeltaPocs[CurrRPListIdx[j]]-slice_pic_order_cnt_lsb+PicOrderCntVal)            if DeltaPocMsbPresentFlag [i-NumDeltaPocs[CurrRPListIdx[j]]            is equal to 1 Or is set equal to            DPocLt[NumDeltaPocs[CurrRPListIdx[j]] otherwise (when            DeltaPocMsbPresentFlag [i-NumDeltaPocs[CurrRPListIdx[j]] is            equal to 0).        -   The value of slice_pic_order_cnt_lsb for the generated            picture is inferred to be equal to ((PicOrderCntVal for the            generated picture) & (MaxPicOrderCntLsb−1)).        -   The generated picture is marked as “used for long-term            reference”.        -   RefPics[j][i] is set to be the generated reference picture.    -   In an example the above steps may be performed for j equal to        num_rpl_slice_header_minus1 only.    -   Based on the syntax provided above in Table 13 and Table 14, in        one example, constructing the reference picture lists        RefPicList0 and, for B slices, RefPicList1 may be as performed        based on the following:    -   The variable NumRpsCurrList0 is set equal to        Max(num_ref_idx_l0_active_minus1+1,        NumDeltaPocs[CurrRPListIdx[0]]+NumPocLtCurr) and the list        RefPicList0 is constructed as follows:

   for( i = 0, rIdx=0; i < (NumDeltaPocs[ CurrRPListIdx[0] ] ]+NumPocLtCurr) && rIdx < NumRpsCurrList0; rIdx++, i++ )   RefPicList0[rIdx ] = RefPics[ 0 ][ i ]

-   -   When the slice is a B slice, the variable NumRpsCurrList1 is set        equal to Max(num_ref_idx_l1_active_minus1+1,        NumDeltaPocs[CurrRPListIdx[0]]+NumPocLtCurr)) and the list        RefPicList1 is constructed as follows:

  for( i = 0, rIdx=0; i < (NumDeltaPocs[ CurrRPListIdx[1] ]+NumPocLtCurr)  &&  rIdx < NumRpsCurrList1; rIdx++, i++ )       RefPicList1[ rIdx ] = RefPics[ 1 ] [ i ]

In one example, the long-term reference picture may be inserted in thereference picture list 0 and/or reference picture list 1 according totheir PicOrderCntVal value distance compared to the PicOrderCntVal ofthe current picture.

It should be noted that with respect to the example illustrated inTables 8-14, processes the generation of one unavailable picture andreference picture list selection may be similar to that described abovewith respect Tables 4-7.

-   -   As described above, a process for reference picture lists        construction of RefPicList0 and RefPicList1 includes determining        respective values for NumRpsCurrList0 and NumRpsCurrList1. As        provided above, values for NumRpsCurrList0 and NumRpsCurrList1        are determined based on respective values of        num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1.        In JVET-K1001 values of num_ref_idx_l0_active_minus1 and        num_ref_idx_l1_active_minus1 may be determined based on the        following syntax elements included in the picture parameter set        (PPS).    -   num_ref_idx_l0_default_active_minus1 specifies the inferred        value of num_ref_idx_l0_active_minus1 for P and B slices with        num_ref_idx_active_override_flag equal to 0. The value of        num_ref_idx_l0_default_active_minus1 shall be in the range of 0        to 14, inclusive.    -   num_ref_idx_l1_default_active_minus1 specifies the inferred        value of num_ref_idx_l1_active_minus1 with        num_ref_idx_active_override_flag equal to 0. The value of        num_ref_idx_l1_default_active_minus1 shall be in the range of 0        to 14, inclusive.    -   and the following syntax elements provided in the slice_header:    -   num_ref_idx_active_override_flag equal to 1 specifies that the        syntax element num_ref_idx_l0_active_minus1 is present for P and        B slices and that the syntax element        num_ref_idx_l1_active_minus1 is present for B slices.        num_ref_idx_active_override_flag equal to 0 specifies that the        syntax elements num_ref_idx_l0_active_minus1 and        num_ref_idx_l1_active_minus1 are not present.    -   num_ref_idx_l0_active_minus1 specifies the maximum reference        index for reference picture list 0 that may be used to decode        the slice. num_ref_idx_l0_active_minus1 shall be in the range of        0 to 14, inclusive. When the current slice is a P or B slice and        num_ref_idx_l0_active_minus1 is not present,        num_ref_idx_l0_active_minus1 is inferred to be equal to        num_ref_idx_l0_default_active_minus1.

num_ref_idx_l1_active_minus1 specifies the maximum reference index forreference picture list 1 that may be used to decode the slice.num_ref_idx_l1_active_minus1 shall be in the range of 0 to 14,inclusive. When num_ref_idx_l1_active_minus1 is not present,num_ref_idx_l1_active_minus1 is inferred to be equal tonum_ref_idx_l1_default_active_minus1.

-   -   According to the techniques herein,        num_ref_idx_l0_default_active_minus1, and        num_ref_idx_l1_default_active_minus1 may be removed from the PPS        in JVET-K1001, and variations of the PPS including        num_ref_idx_l0_default_active_minus1, and        num_ref_idx_l1_default_active_minus1.        num_ref_idx_active_override_flag, num_ref_idx_l0_active_minus1,        and num_ref_idx_l1_active_minus1 may be removed from the slice        header in JVET-K1001, and variations of the slice header        including num_ref_idx_active_override_flag,        num_ref_idx_l0_active_minus1, and num_ref_idx_l1_active_minus1.        That is, according to the techniques herein values of        num_ref_idx_l0_active_minus1, and num_ref_idx_l1_active_minus1        are derived instead of being signaled directly. Further,        techniques for deriving values corresponding to        num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1        according to techniques herein are described below. It should be        noted that the conventions in ITU-T H.265 and JVET-K1001 provide        where signaled values in calculations include underscores and        derived values, which are called variables, do not include        underscores. Thus, in the equations below NumRefIdxL0ActiveMinus        is a derived variable, the value of which corresponds to the        previously signalled value of num_ref_idx_l0_active_minus1 and        NumRefIdxL1ActiveMinus is a derived variable, the value of which        corresponds to the previously signalled value        num_ref_idx_l1_active_minus1. It should be noted that when the        techniques described herein are used to modify JVET-K1001        instances of num_ref_idx_l0_active_minus1 and        num_ref_idx_l1_active_minus1 in JVET-K1001 are replaced with        respective instances of NumRefIdxL0ActiveMinus and        NumRefIdxL1ActiveMinus. For the sake of brevity, each respective        replacement of num_ref_idx_l0_active_minus1 and        num_ref_idx_l1_active_minus1 with NumRefIdxL0ActiveMinus and        NumRefIdxL1ActiveMinus is not described in detail herein.    -   In one example, according to the techniques herein,        NumRefIdxL0ActiveMinus and NumRefIdxL1ActiveMinus may be derived        as follows:    -   If current slice is a P or B slice:

    NumRefIdxL0ActiveMinus  =  (rpl_sps_flag?  NumDeltaPocs[ rpl_idx[0]] :  NumDeltaPocs[num_ref_pic_lists_minus1+1] )−1

-   -   If current slice is a B slice:

    NumRefIdxLlActiveMinus  =  (rpl_sps_flag?  NumDeltaPocs[ rpl_idx[1] ] : NumDeltaPocs[num_ref_pic_lists_minus1+2])−1

-   -   Further, in one example, according to the techniques herein,        num_ref_idx_l0_active_minus1 and num_ref_idx_l1_active_minus1        may be derived as follows:    -   If current slice is a P or B slice:

   NumRefIdxL0ActiveMinus       =     (rpl_sps_flag? (NumDeltaPocs[    rpl_idx[0]]+NumPocLt[   rpl_idx[0]]    :(NumDeltaPocs[num_ref_pic_lists_minus1+1]+NumPocLt[num_ref_pic_lists_minus1+1] ))−1

-   -   If current slice is a B slice:

   NumRefIdxL1ActiveMinus       =     (rpl_sps_flag? (NumDeltaPocs[   rpl_idx[1]]+NumPocLt [    rpl_idx[0]])  :NumDeltaPocs[num_ref_pic_lists_minus1+2]+NumPocLt[num_ref_pic_lists_minus1+2] )−1

It should be noted that in one example, in the equations above, the stepof subtracting 1 to derive NumRefIdxL0ActiveMinus andNumRefIdxL1ActiveMinus may be omitted.

-   -   Additionally, in this case the reference picture list 0 and        reference picture list 1 creation process will be modified as        follows:        -   The list RefPicList0 is constructed as follows:

   for(i = 0; i < (NumDeltaPocs[ CurrRPListIdx[0] ] ]+NumPocLt[CurrRPListIdx[0]]); i++ )        RefPicList0[ rIdx ] = RefPics[ 0 ][ i ]

-   -   -   When the slice is a B slice, the list RefPicList1 is            constructed as follows:

for(i         =        0;        i   < (NumDeltaPocs[ CurrRPListIdx[1]]+NumPocLt[ CurrRPListIdx[1]]); i++ )        RefPicList1[ rIdx ] =RefPics[ 1 ][ i ]

In another example, additionally, in this case the reference picturelist 0 and reference picture list 1 creation process will be modified asfollows:

-   -   The list RefPicList0 is constructed as follows:

  for(i = 0; i < NumDeltaPocs[ CurrRPListIdx[0] ] ; i++ )    RefPicList0[ rIdx ] = RefPics[ 0 ][ i ]

-   -   When the slice is a B slice, the list RefPicList1 is constructed        as follows:

  for(i = 0; i < NumDeltaPocs[ CurrRPListIdx[1] ]; i++ )    RefPicList1[ rIdx ] = RefPics[ 1 ] [ i ]

“On reference picture management for VVC,” 12th Meeting of ISO/IECJTC1/SC29/WG11 3-12 Oct. 2018, Macao, CN, document JVET-L0112-v3, whichis referred to herein as JVET-L0112, describes a reference picturemanagement approach based on direct signaling and derivation ofreference picture lists 0 and 1. In particular, Table 15 illustrates therelevant syntax included in the SPS for the reference picture managementapproach described in JVET-L0112, Table 16 illustrates the relevantsyntax included in the PPS for the reference picture management approachdescribed in JVET-L0112, and Table 17 illustrates the relevant syntaxincluded in the slice header for the reference picture managementapproach described in JVET-L0112.

TABLE 15 Descriptor seq_parameter_set_rbsp( ) { ... long_term_ref_pics_flag u(1)  if( long_term_ref_pics_flag ) additional_lt_poc_lsb ue(v)  rpl1_same_as_rpl0_flag u(1)  for( i = 0; i< !rpl1_same_as_rpl0_flag ? 2 : 1; i++ ) {   num_ref_pic_lists_in_sps[ i] ue(v)   for( j = 0; j < num_ref_pic_lists_in_sps[ i ]; j++)   ref_pic_list_struct( i, j, long_term_ref_pics_flag )  } ... }

TABLE 16 Descriptor pic_parameter_set_rbsp( ) { ...  for( i = 0; i < 2;i++)  num_ref_idx_default_active_minus1[ i ] ue(v) rpl1_idx_present_flag u(1) ...  rbsp_trailing_bits( ) }

TABLE 17 Descriptor slice_header( ) { ...  if( nal_unit_type != IRAP_NUT) {   slice_pic_order_cnt_lsb u(v)   for( i = 0; i < 2; i++ ) {    if( i= = 0 ∥ ( i = = 1 && rpl1_idx_present_flag ) )    ref_pic_list_sps_flag[ i ] u(1)    if( ref_pic_list_sps_flag[ i ] ){     if( num_ref_pic_lists_in_sps[ i ] > 1 )      if( i = = 0 ∥ ( i = =1 && rpl1_idx_present_flag ) )       ref_pic_list_idx[ i ] u(v)    }else     ref_pic_list_struct( i, num_ref_pic_lists_in_sps[ i ],long_term_ref_pics_flag )   }   if( slice_type = = P ∥ slice_type = = B) {    num_ref_idx_active_override_flag u(1)    if(num_ref_idx_active_override_flag )     for( i = 0; i < ( slice_type = =B ? 2: 1 ); i++ )      num_ref_idx_active_minus1[ i ] ue(v)   }  }  ...}

-   -   JVET-L0112 provides the following definitions for the respective        syntax elements illustrated in Table 15:    -   long_term_ref_pics_flag equal to 0 specifies that no LTRP is        used for inter prediction of any coded picture in the CVS.        long_term_ref_pics_flag equal to 1 specifies that LTRPs may be        used for inter prediction of one or more coded pictures in the        CVS.    -   additional_lt_poc_lsb specifies the value of the variable        MaxLtPicOrderCntLsb that is used in the decoding process for        reference picture lists as follows:

MaxLtPicOrderCntLsb=2^((log2_max_pic_order_cnt_lsb_minus4+4+additional_lt_poc_lsb))

-   -   The value of additional_lt_poc_lsb shall be in the range of 0 to        32−log2_max_pic_order_cnt_lsb_minus4−4, inclusive.    -   When not present, the value of additional_lt_poc_lsb is inferred        to be equal to 0.    -   rpl1_same_as_rpl0_flag equal to 1 specifies that the syntax        structures num_ref_pic_lists_in_sps[1] and        ref_pic_list_struct(1, rplsIdx, ltrpFlag) are not present and        the following applies:        -   The value of num_ref_pic_lists_insps[1] is inferred to be            equal to the value of num_ref_pic_lists_in_sps[0].        -   The value of each of syntax elements in            ref_pic_list_struct(1, rplsIdx, ltrpFlag) is inferred to be            equal to the value of corresponding syntax element in            ref_pic_list_struct(0, rplsIdx, ltrpFlag) for rplsIdx            ranging from 0 to num_ref_pic_lists_in_sps[0]−1.    -   num_ref_pic_lists_in_sps[i] specifies the number of the        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structures with listIdx equal to i included in the SPS. The        value of num_ref_pic_lists_in_sps[i] shall be in the range of 0        to 64, inclusive.        -   NOTE 2—For each value of listIdx (equal to 0 or 1), a            decoder should allocate memory for a total number of            num_ref_pic_lists_in_sps[i]+1 ref_pic_list_struct(listIdx,            rplsIdx, ltrpFlag) syntax structures since there may be one            ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax            structure directly signalled in the slice headers of a            current picture.

NET-L0112 provides the following definitions for the respective syntaxelements illustrated in Table 16:

-   -   num_ref_idx_default_active_minus1[i] plus 1, when i is equal to        0, specifies the inferred value of the variable        NumRefIdxActive[0] for P or B slices with        num_ref_idx_active_override_flag equal to 0, and, when i is        equal to 1, specifies the inferred value of NumRefIdxActive[1]        for B slices with num_ref_idx_active_override_flag equal to 0.        The value of num_ref_idx_default_active_minus1[i] shall be in        the range of 0 to 14, inclusive.    -   rpl1_idx_present_flag equal to 0 specifies that        ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not present        in slice headers. rpll_idx_present_fiag equal to 1 specifies        that ref_pic_list_sps_fiag[1] and ref_pic_list_idx[1] may be        present in slice headers.

JVET-L0112 provides the following definitions for the respective syntaxelements illustrated in Table 17:

-   -   slice_pic_order_cnt_lsb specifies the picture order count modulo        MaxPicOrderCntLsb for the current picture. The length of the        slice_pic_order_cnt_lsb syntax element is        log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of the        slice_pic_order_cnt_lsb shall be in the range of 0 to        MaxPicOrderCntLsb−1, inclusive. When slice_pic_order_cnt_lsb is        not present, slice_pic_order_cnt_lsb is inferred to be equal to        0.    -   ref_pic_list_sps_flag[i] equal to 1 specifies that reference        picture list i of the current picture is derived based on one of        the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structures with listIdx equal to i in the active SPS.        ref_pic_list_sps_flag[i] equal to 0 specifies that reference        picture list i of the current picture is derived based on the        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure        with listIdx equal to i that is directly included in the slice        headers of the current picture. When num_ref_pic_lists_in_sps[i]        is equal to 0, the value of ref_pic_list_sps_flag[i] shall be        equal to 0. When rpl_idx_present_flag is equal to 0 and        ref_pic_list_sps_flag[0] is present, the value of        ref_pic_list_sps_flag[1] is inferred to be equal to        ref_pic_list_sps_flag[0].    -   ref_pic_list_idx[i] specifies the index, into the list of the        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structures with listIdx equal to i included in the active SPS,        of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structure with listIdx equal to i that is used for derivation of        reference picture list i of the current picture. The syntax        element ref_pic_list_idx[i] is represented by        Ceil(Log2(num_ref_pic_lists_in_sps[i])) bits. When not present,        the value of ref_pic_list_idx[i] is inferred to be equal to 0.        The value of ref_pic_list_idx[i] shall be in the range of 0 to        num_ref_pic_lists_in_sps[i]−1, inclusive. When        rpl_idxpresent_flag is equal to 0 and ref_pic_list_sps_flag[0]        is present, the value of ref_pic_list_idx[1] is inferred to be        equal to ref_pic_list_idx[0].    -   num_ref_idx_active_override_flag equal to 1 specifies that the        syntax element num_ref_idx_active_minus1[0] is present for P and        B slices and that the syntax element        num_ref_idx_active_minus1[1] is present for B slices.        num_ref_idx_active_override_flag equal to 0 specifies that the        syntax elements num_ref_idx_active_minus1[0] and        num_ref_idx_active_minus1[1] are not present.    -   num_ref_idx_active_minus1[i], when present, specifies the value        of the variable NumRefIdxActive[i] as follows:

  NumRefIdxActive[ i ] = num_ref_idx_active_minus1[ i ] + 1

The value of num_ref_idx_active_minusl[i] shall be in the range of 0 to14, inclusive.

-   -   The value of NumRefIdxActive[i]−1 specifies the maximum        reference index for reference picture list i that may be used to        decode the slice. When the value of NumRefIdxActive[i] is equal        to 0, no reference index for reference picture list i may be        used to decode the slice.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[i] is inferred to be equal to        num_ref_idx_default_active_minus1[i]+1.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[0] is inferred to be equal to        num_ref_idx_default_active_minus1[0]+1.    -   When the current slice is a P slice, NumRefIdxActive[1] is        inferred to be equal to 0.    -   When the current slice is an I slice, both NumRefIdxActive[0]        and NumRefIdxActive[1] are inferred to be equal to 0.

In one example, according to the techniques herein, the slice header inJVET-L0112 may be modified to such that when the syntax elementscorresponding to the number of active reference pictures are needed tobe signaled, they are only signaled when the corresponding referencepicture list includes more than one entry. In this case, when notsignaled the number of active reference pictures for reference picturelist 0 and/or reference picture list 1 are inferred. This provides bitsavings.

In particular, Table 18 illustrates an example of the relevant syntaxincluded in the slice header according to the techniques herein.

TABLE 18 Descriptor slice_header( ) { ...  if( nal_unit_type != IRAP_NUT) {   slice_pic_order_cnt_lsb u(v)   for( i = 0; i < 2; i++ ) {    if( i= = 0 ∥ (i = = 1 && rpl1_idx_present_flag ) )     ref_pic_list_sps_flag[i ] u(1)    if( ref_pic_list_sps_flag[ i ] ) {     if(num_ref_pic_lists_in_sps[ i ] > 1 )      if( i = = 0 ∥ (i = = 1 &&rpl1_idx_present_flag ) )       ref_pic_list_idx[ i ] u(v)    } else    ref_pic_list_struct( i, num_ref_pic_lists_in_sps[ i ],long_term_ref_pics_flag )   }   if( slice_type = = P ∥ slice_type = = B) {    num_ref_idx_active_override_flag u(1)    if(num_ref_idx_active_override_flag )     for( i = 0; i < ( slice_type = =B ? 2: 1 ); i++ )      if( ref_pic_list_sps_flag[ i ] )       currRplsIdx[ i ] = ref_pic_list_idx[ i ]      else       currRplsIdx[ i ] = num_ref_pic_lists_in_sps[ i ]      if(NumEntriesInList[ i ][ currRplsIdx[i] ]>1)        num_ref_idx_active_minus1[ i ] ue(v)   }  }  ... }

With respect to the respective syntax elements illustrated in Table 18,the definitions may be based on the definitions provided above. Withrespect to the syntax element num_ref_idx_active_minus1 the definitionmay be based on the following:

-   -   num_ref_idx_active_minus1[i], when present, specifies the value        of the variable NumRefIdxActive[i] as follows:        -   NumRefIdxActive[i]=num_ref_idx_active_minus1[i]+1    -   The value of num_ref_idx_active_minus1[i] shall be in the range        of 0 to 14, inclusive.    -   The value of NumRefIdxActive[i]−1 specifies the maximum        reference index for reference picture list i that may be used to        decode the slice. When the value of NumRefIdxActive[i] is equal        to 0, no reference index for reference picture list i may be        used to decode the slice.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[i] is inferred to be equal to        num_ref_idx_default_active_minus1[i]+1.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[0] is inferred to be equal to        num_ref_idx_default_active_minus1[0]+1.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 1, and        num_ref_idx_active_minus1[i] is not present,        num_ref_idx_active_minus1 [i] is inferred to be equal to 0. In        another example a different value may be inferred for        num_ref_idx_active_minus1 [i] for I equal to 0 and 1.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 1,        num_ref_idx_activeminus1[0] is not present,        num_ref_idx_active_minus1[0] is inferred to be equal to 0. In        another example, a different value may be inferred for        num_ref_idx_active_minus1[0].    -   When the current slice is a P slice, NumRefIdxActive[1] is        inferred to be equal to 0.    -   When the current slice is an I slice, both NumRefIdxActive[0]        and NumRefIdxActive[1] are inferred to be equal to 0.    -   Further, in one example, according to the techniques herein, in        Tables 17 num_ref_idx_active_minus1[i] may be instead be        signaled as num_ref_idx_active[i], to allow a reference picture        list to have no active reference pictures for a current picture.        This may be the case when that reference picture list only        includes pictures which are reference pictures for future        pictures in the bitstream. Another case where a reference        picture list may be empty may be when        num_strp_entries[listIdx][rplsIdx] and        num_ltrp_entries[listIdx][rplsIdx] are signaled in        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) such that the        value of NumEntrieslnList[listIdx][rplsIdx] shall be in the        range of 0 to sps_max_dec_pic_buffering_minus1. In one example,        num_ref_idx_active [i] may be based on the following definition:    -   num_ref_idx_active [i], when present, specifies the value of the        variable NumRefIdxActive[i] as follows:        -   NumRefIdxActive[i]=num_ref_idx_active[i]    -   The value of num_ref_idx_active[i] shall be in the range of 0 to        15, inclusive.    -   When num_ref_idx_active[i] is greater than 0, the value of        NumRefIdxActive[i]specifies the maximum reference index for        reference picture list i that may be used to decode the slice.        When the value of NumRefIdxActive[i] is equal to 0, no reference        index for reference picture list i may be used to decode the        slice.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[i] is inferred to be equal to        num_ref_idx_default_active_minus1[i]+1.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[0] is inferred to be equal to        num_ref_idx_default_active_minus1[0]+1.    -   When the current slice is a P slice, NumRefIdxActive[1] is        inferred to be equal to 0.    -   When the current slice is an I slice, both NumRefIdxActive[0]        and NumRefIdxActive[1] are inferred to be equal to 0.

Further, in one example, according to the techniques herein, in Table 18may be modified and signaled as in Table 18A. In this case,num_ref_idx_active_minus1[i] may be instead be signaled as num_ref_idxactive[i] to allow a reference picture list to have no active referencepictures for a current picture. This may be the case when that referencepicture list only includes pictures which are reference pictures forfuture pictures in the bitstream. Another case where a reference picturelist may be empty may be when num_strp_entries[listIdx][rplsIdx] andnum_ltrp_entries[listIdx][rplsIdx] are signaled inref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) such that the value ofNumEntriesInList[listIdx][rplsIdx] shall be in the range of 0 tosps_max_dec_pic_buffering_minus1. In one example, num_ref_idx active [i]may be based on the following definition. Additionally, in this casewhen the syntax elements corresponding to the number of active referencepictures are needed to be signaled, they are only signaled when thecorresponding reference picture list is not empty. In this case, whennot signaled the number of active reference pictures for referencepicture list 0 and/or reference picture list 1 are inferred. Thisprovides bit savings.

TABLE 18A Descriptor slice_header( ) {  slice_pic_parameter_set_id ue(v) slice_address u(v)  slice_type ue(v)  if( nal_unit_type != IRAP_NUT ) {  slice_pic_order_cnt_lsb u(v)   for( i = 0; i < 2; i++ ) {    if( i = =0 ∥ ( i = = 1 && rpl1_idx_present_flag ) )     ref_pic_list_sps_flag[ i] u(1)    if( ref_pic_list_sps_flag[ i ] ) {     if(num_ref_pic_lists_in_sps[ i ] > 1 )      if( i = = 0 ∥ ( i = = 1 &&rpl1_idx_present_flag ) )       ref_pic_list_idx[ i ] u(v)    } else    ref_pic_list_struct( i, num_ref_pic_lists_in_sps[ i ],long_term_ref_pics_flag )   }   if( slice_type = = P ∥ slice_type = = B) {    num_ref_idx_active_override_flag u(1)    if(num_ref_idx_active_override_flag )     for( i = 0; i < ( slice_type = =B ? 2: 1 ); i++ ) {      if( ref_pic_list_sps_flag[ i ] )       currRplsIdx[ i ] = ref_pic_list_idx[ i ]      else       currRplsIdx[ i ] = num_ref_pic_lists_in_sps[ i ]     if(NumEntriesInList[ i ][ currRplsIdx[i] ]>0)      num_ref_idx_active [ i ] ue(v)      }   }  } ... }

-   -   In this case the semantics may be as follows:    -   num_ref_idx_active[i], when present, specifies the value of the        variable NumRefIdxActive[i] as follows:        -   NumRefIdxActive[i]=num_ref_idx_active[i]        -   The value of num_ref_idx_active[i] shall be in the range of            0 to 15, inclusive.    -   When num_ref_idx_active[i] is greater than 0, the value of        NumRefIdxActive[i] specifies the maximum reference index for        reference picture list i that may be used to decode the slice.        When the value of NumRefIdxActive[i] is equal to 0, no reference        index for reference picture list i may be used to decode the        slice.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[i] is inferred to be equal to        num_ref_idx_default_active_minus1[i]+1.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 0,        NumRefIdxActive[0] is inferred to be equal to        num_ref_idx_default_active_minus1[0]+1.    -   For i equal to 0 or 1, when the current slice is a B slice and        num_ref_idx_active_override_flag is equal to 1, and        num_ref_idx_active[i] is not present, num_ref_idx_active[i] is        inferred to be equal to 0.    -   When the current slice is a P slice and        num_ref_idx_active_override_flag is equal to 1,        num_ref_idx_active[0] is not present, num_ref_idx_active[0] is        inferred to be equal to 0.    -   When the current slice is a P slice, NumRefIdxActive[1] is        inferred to be equal to 0.    -   When the current slice is an I slice, both NumRefIdxActive[0]        and NumRefIdxActive[1] are inferred to be equal to 0.

In another example, the constraint onNumEntrieslnList[listIdx][rplsIdx]=num_strp_entries[listIdx][rplsIdx]+num_ltrp_entries[listIdx][rplsIdx]may be modified as follows:

-   -   The value of NumEntrieslnList[listIdx][rplsIdx] shall be in the        range of 01 to sps_max_dec_pic_buffering_minus1, inclusive.

Referring to Table 5 above, in one example, according to the techniquesherein, in one example, the active override syntax may be included inthe slice header according to the example illustrated in Table 19.

TABLE 19 Descriptor slice_header( ) {  ...   num_rpl_slice_header_minus1 u(2)    rpl_sps_flag u(1)    if(!rpl_sps_flag ) {     for( i = num_ref_pic_lists_minus1+1; i <num_ref_pic_lists_minus1+num_rpl_slice_header_minus1+2; i++)     pic_list(i)    }    else {     for( j = 0; j <num_rpl_slice_header_minus1+1; j++)      rpl_index[j] u(v)    }   if(slice_type = = P ∥ slice_type = = B ) {   num_ref_idx_active_override_flag u(1)    if(num_ref_idx_active_override_flag ) {     if(NumDeltaPocs[CurrRPListIdx[0] ]>1)       num_ref_idx_l0_active_minus1 ue(v)     if((slice_type = = B) && (NumDeltaPocs[ CurrRPListIdx[1] ]>1) )     num_ref_idx_l1_active_minus1 ue(v)    } ...  byte_alignment( ) }

-   -   With respect to the respective syntax elements illustrated in        Table 19, the definitions may be based on the definitions        provided above. With respect to the syntax element        num_ref_idx_activeminus1 the definition may be based on the        following:    -   num_ref_idx_l0_active_minus1 specifies the maximum reference        index for reference picture list 0 that may be used to decode        the slice. num_ref_idx_l0_active_minus1 shall be in the range of        0 to 14, inclusive. When the current slice is a P or B slice and        num_ref_idx_active_override_flag is equal to 0,        num_ref_idx_l0_active_minus1 is inferred to be equal to        num_ref_idx_l0_default_active_minus1.    -   When the current slice is a P or B slice and        num_ref_idx_active_override_flag is equal to 1 and        num_ref_idx_l0_active_minus1 is not present,        num_ref_idx_l0_active_minus1 is inferred to be equal to 0.    -   num_ref_idx_l1_active_minus1 specifies the maximum reference        index for reference picture list 1 that may be used to decode        the slice. num_ref_idx_l1_active_minus1 shall be in the range of        0 to 14, inclusive. When num_ref_idx_l1_active_minus1 is not        present and num_ref_idx_active_override_flag is equal to 0,        num_ref_idx_l1_active_minus1 is inferred to be equal to        num_ref_idx_l1_default_active_minus1.    -   When num_ref_idx_l1_active_minus1 is not present and        num_ref_idx_active_override_fiag is equal to 1,        num_ref_idx_l1_active_minus1 is inferred to be equal to 0.

With respect to Table 19, the following part of the syntax

if( (slice_type = = B) && (NumDeltaPocs[ CurrRPListIdx[1] ]>1) ) num_ref_idx_l1_active_minus1 ue(v)

-   -   may instead be written equivalently as:

 if( (slice_type = = B) ) {   if(NumDeltaPocs[ CurrRPListIdx[1] ]>1)  num_ref_idx_l1_active_minus1 ue(v) }

Table 20 illustrates the relevant syntax for reference picture liststructure included for the reference picture management approachdescribed in JVET-L0112.

TABLE 20 Descriptor ref_pic_list_struct( listIdx, rplsIdx, ltrpFlag ) { num_strp_entries[ listIdx ][ rplsIdx ] ue(v)  if( ltrpFlag)  num_ltrp_entries[ listIdx ][ rplsIdx ] ue(v)  for( i = 0; i <NumEntriesInList[ listIdx ][ rplsIdx ]; i++) {   if( num_ltrp_entries[listIdx ][ rplsIdx ] > 0 )    lt_ref_pic_flag[ listIdx ][ rplsIdx ][ i ]  if( !lt_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] ) {   strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] u(1)    delta_poc_st[listIdx ][ rplsIdx ][ i ] ue(v)   } else    poc_lsb_lt[ listIdx ][rplsIdx ][ i ] u(v)  } }

-   -   JVET-L0112 provides the following definitions for the respective        syntax elements illustrated in Table 20:    -   The ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structure may be present in an SPS or in a slice_header.        Depending on whether the syntax structure is included in a        slice_header or an SPS, the following applies:        -   If present in a slice_header, the            ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax            structure specifies reference picture list listIdx of the            current picture (the picture containing the slice).        -   Otherwise (present in an SPS), the            ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax            structure specifies a candidate for reference picture list            listIdx, and the term “the current picture” in the semantics            specified in the remainder of this clause refers to each            picture that 1) has one or more slices containing            ref_pic_list_idx[listIdx] equal to an index into the list of            the ref_pie_list_struct(listIdx, rplsIdx, ltrpFlag) syntax            structures included in the SPS, and 2) is in a CVS that has            the SPS as the active SPS.    -   num_strp_entries[listIdx][rplsIdx] specifies the number of STRP        entries in the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag)        syntax structure.    -   num_ltrp_entries[listIdx][rplsIdx] specifies the number of LTRP        entries in the ref_pic_liststruct(listIdx, rplsIdx, ltrpFlag)        syntax structure. When not present, the value of        num_ltrp_entries[listIdx][rplsIdx] is inferred to be equal to 0.    -   The variable NumEntriesInList[listIdx][rplsIdx] is derived as        follows:

  NumEntriesInList[ listIdx ][ rplsIdx ] = num_strp_entries[ listIdx ]       [ rplsIdx ] + num_ltrp_entries[ listIdx ][ rplsIdx ]

-   -   The value of NumEntriesInList[listIdx][rplsIdx] shall be in the        range of 0 to sps_max_dec_pic_buffering_minus1, inclusive.    -   lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 1 specifies that        the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx,        ltrpFlag) syntax structure is an LTRP entry.        lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 0 specifies that        the i-th entry in the ref_pic_list_struct(listIdx, rplsIdx,        ltrpFlag) syntax structure is an STRP entry. When not present,        the value of Itref_pic_flag[listIdx][rplsIdx][i] is inferred to        be equal to 0.    -   It is a requirement of bitstream conformance that the sum of        lt_ref_pic_flag[listIdx][rplsIdx][i] for all values of i in the        range of 0 to NumEntriesInList[listIdx][rplsIdx]−1, inclusive,        shall be equal to numltrp_entries[listIdx][rplsIdx].    -   strp_entry_sign_flag[listIdx][rplsIdx][i] equal to 1 specifies        that i-th entry in the syntax structure        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) has a value        greater than or equal to 0.        strp_entry_sign_flag[listIdx][rplsIdx] equal to 0 specifies that        the i-th entry in the syntax structure        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) has a value less        than 0.    -   delta_poc_st[listIdx][rplsIdx][i], when the i-th entry is the        first STRP entry in ref_pic_list_struct(rplsIdx, ltrpFlag)        syntax structure, specifies the absolute difference between the        picture order count values of the current picture and the        picture referred to by the i-th entry, or, when the i-th entry        is an STRP entry but not the first STRP entry in the        ref_pic_list_struct(rplsIdx, ItrpFlag) syntax structure,        specifies the absolute difference between the picture order        count values of the pictures referred to by the i-th entry and        by the previous STRP entry in the ref_pic_list_struct(listIdx,        rplsIdx, ltrpFlag) syntax structure.

The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of−2¹⁵ to 2¹⁵−1 inclusive.

-   -   The list DeltaPocSt[listIdx][rplsIdx] is derived as follows:

for( i = 0; i < NumEntriesInList[ listIdx ][ rplsIdx ]; i++) {      if(!lt_ref_pic_flag[ i ][ RplsIdx[ i ] ][ j ]) {        DeltaPocSt[ listIdx][ rplsIdx ][ i ] = ( strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ]) ?             delta_poc_st[ listIdx ][ rplsIdx ][ i ] : 0 − delta_poc_st[listIdx ][ rplsIdx ][ i ]    } }

-   -   poc_lsb_lt[listIdx][rplsIdx][i] specifies the value of the        picture order count modulo MaxLtPicOrderCntLsb of the picture        referred to by the i-th entry in the        ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax        structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i]        syntax element is Log2(MaxLtPicOrderCntLsb) bits.

In one example, according to the techniques herein, the relevant syntaxfor a reference picture list structure may be modified as shown in Table21, such that the syntax element for number of short term referencepicture entries is modified to be signaled with a minus1 coding. Thisprovides bit savings and requires that at least one short term referencepicture is signaled.

TABLE 21 Descriptor ref_pic_list_struct( listIdx, rplsIdx, ltrpFlag ) { num_strp_entries_minus1[ listIdx ][ rplsIdx ] ue(v)  if( ltrpFlag )  num_ltrp_entries[ listIdx ][ rplsIdx ] ue(v)  for( i = 0; i <NumEntriesInList[ listIdx ][ rplsIdx ]; i++) {   if( num_ltrp_entries[listIdx ][ rplsIdx ] > 0 )    lt_ref_pic_flag[ listIdx ][ rplsIdx ][ i ]  if( !lt_ref_pic_flag[ listIdx ][ rplsIdx ][ i ] ) {   strp_entry_sign_flag[ listIdx ][ rplsIdx ][ i ] u(1)    delta_poc_st[listIdx ][ rplsIdx ][ i ] ue(v)   } else    poc_lsb_lt[ listIdx ][rplsIdx ][ i ] u(v)  } }

In this case, the semantics for num_strp_entries_minus1 in Table 21 mayas follows:

-   -   num_strp_entries_minus1[listIdx][rplsIdx] plus 1 specifies the        number of STRP entries in the ref_pic_list_struct(listIdx,        rplsIdx, ltrpFlag) syntax structure.

In this case, the variable NumEntrieslnList[listIdx][rplsIdx] may bederived as follows:

-   -   NumEntrieslnList[listIdx][rplsIdx]=num_strp_entries_minus1[listIdx][rplsIdx]+1+num_ltrp_entries[listIdx][rplsIdx]

In another example, this constraint may be as follows:

-   -   The value of NumEntrieslnList[listIdx][rplsIdx] shall be in the        range of 1 to sps_max_decpic_buffering_minus1, inclusive.    -   OR as follows:    -   The value of NumEntriesInList[listIdx][rplsIdx] shall be greater        than 0.

In this manner, source device 102 represents an example of a deviceconfigured to signal one or more candidate reference picture lists in aparameter set, and signal an index to one of the candidate referencepicture lists in a header associated with a region of a picture.

Referring again to FIG. 1 , interface 108 may include any deviceconfigured to receive data generated by data encapsulator 107 andtransmit and/or store the data to a communications medium. Interface 108may include a network interface card, such as an Ethernet card, and mayinclude an optical transceiver, a radio frequency transceiver, or anyother type of device that can send and/or receive information. Further,interface 108 may include a computer system interface that may enable afile to be stored on a storage device. For example, interface 108 mayinclude a chipset supporting Peripheral Component Interconnect (PCI) andPeripheral Component Interconnect Express (PCIe) bus protocols,proprietary bus protocols, Universal Serial Bus (USB) protocols, I²C, orany other logical and physical structure that may be used tointerconnect peer devices.

Referring again to FIG. 1 , destination device 120 includes interface122, data decapsulator 123, video decoder 124, and display 126.Interface 122 may include any device configured to receive data from acommunications medium. Interface 122 may include a network interfacecard, such as an Ethernet card, and may include an optical transceiver,a radio frequency transceiver, or any other type of device that canreceive and/or send information. Further, interface 122 may include acomputer system interface enabling a compliant video bitstream to beretrieved from a storage device. For example, interface 122 may includea chipset supporting PCI and PCIe bus protocols, proprietary busprotocols, USB protocols, I²C, or any other logical and physicalstructure that may be used to interconnect peer devices. Datadecapsulator 123 may be configured to receive and parse any of theexample syntax structures described herein.

Video decoder 124 may include any device configured to receive abitstream (e.g., a MCTS sub-bitstream extraction) and/or acceptablevariations thereof and reproduce video data therefrom. Display 126 mayinclude any device configured to display video data. Display 126 maycomprise one of a variety of display devices such as a liquid crystaldisplay (LCD), a plasma display, an organic light emitting diode (OLED)display, or another type of display. Display 126 may include a HighDefinition display or an Ultra High Definition display. It should benoted that although in the example illustrated in FIG. 1 , video decoder124 is described as outputting data to display 126, video decoder 124may be configured to output video data to various types of devicesand/or sub-components thereof. For example, video decoder 124 may beconfigured to output video data to any communication medium, asdescribed herein.

FIG. 6 is a block diagram illustrating an example of a video decoderthat may be configured to decode video data according to one or moretechniques of this disclosure. In one example, video decoder 600 may beconfigured to decode transform data and reconstruct residual data fromtransform coefficients based on decoded transform data. Video decoder600 may be configured to perform intra prediction decoding and interprediction decoding and, as such, may be referred to as a hybriddecoder. Video decoder 600 may be configured to parse any combination ofthe syntax elements described above in Tables 1-14. Video decoder 600may derive reference picture lists based on or according to theprocesses described above. Video decoder 600 may constructing thereference picture lists RefPicList0 and RefPicList1 based on oraccording to the processes described above. Video decoder may performvideo decoding based on the reference picture lists.

In the example illustrated in FIG. 6 , video decoder 600 includes anentropy decoding unit 602, inverse quantization unit and transformcoefficient processing unit 604, intra prediction processing unit 606,inter prediction processing unit 608, summer 610, post filter unit 612,and reference buffer 614. Video decoder 600 may be configured to decodevideo data in a manner consistent with a video coding system. It shouldbe noted that although example video decoder 600 is illustrated ashaving distinct functional blocks, such an illustration is fordescriptive purposes and does not limit video decoder 600 and/orsub-components thereof to a particular hardware or softwarearchitecture. Functions of video decoder 600 may be realized using anycombination of hardware, firmware, and/or software implementations.

As illustrated in FIG. 6 , entropy decoding unit 602 receives an entropyencoded bitstream. Entropy decoding unit 602 may be configured to decodesyntax elements and quantized coefficients from the bitstream accordingto a process reciprocal to an entropy encoding process. Entropy decodingunit 602 may be configured to perform entropy decoding according any ofthe entropy coding techniques described above. Entropy decoding unit 602may determine values for syntax elements in an encoded bitstream in amanner consistent with a video coding standard. As illustrated in FIG. 6, entropy decoding unit 602 may determine a quantization parameter,quantized coefficient values, transform data, and predication data froma bitstream. In the example, illustrated in FIG. 6 , inversequantization unit and transform coefficient processing unit 604 receivesa quantization parameter, quantized coefficient values, transform data,and predication data from entropy decoding unit 602 and outputsreconstructed residual data.

Referring again to FIG. 6 , reconstructed residual data may be providedto summer 610 Summer 610 may add reconstructed residual data to apredictive video block and generate reconstructed video data. Apredictive video block may be determined according to a predictive videotechnique (i.e., intra prediction and inter frame prediction). Intraprediction processing unit 606 may be configured to receive intraprediction syntax elements and retrieve a predictive video block fromreference buffer 614. Reference buffer 614 may include a memory deviceconfigured to store one or more frames of video data. Intra predictionsyntax elements may identify an intra prediction mode, such as the intraprediction modes described above. Inter prediction processing unit 608may receive inter prediction syntax elements and generate motion vectorsto identify a prediction block in one or more reference frames stored inreference buffer 616. Inter prediction processing unit 608 may producemotion compensated blocks, possibly performing interpolation based oninterpolation filters. Identifiers for interpolation filters to be usedfor motion estimation with sub-pixel precision may be included in thesyntax elements. Inter prediction processing unit 608 may useinterpolation filters to calculate interpolated values for sub-integerpixels of a reference block. Post filter unit 614 may be configured toperform filtering on reconstructed video data. For example, post filterunit 614 may be configured to perform deblocking and/or Sample AdaptiveOffset (SAO) filtering, e.g., based on parameters specified in abitstream. Further, it should be noted that in some examples, postfilter unit 614 may be configured to perform proprietary discretionaryfiltering (e.g., visual enhancements, such as, mosquito noisereduction). As illustrated in FIG. 6 , a reconstructed video block maybe output by video decoder 600. In this manner, video decoder 600represents an example of a device configured to parse one or more syntaxelements included in a parameter set, the syntax elements indicating oneor more candidate reference picture lists, parse an index from a headerassociated with a region of a picture, the index indicating one of thecandidate reference picture lists, and generate video data based on theindicated candidate reference picture list.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Moreover, each functional block or various features of the base stationdevice and the terminal device used in each of the aforementionedembodiments may be implemented or executed by a circuitry, which istypically an integrated circuit or a plurality of integrated circuits.The circuitry designed to execute the functions described in the presentspecification may comprise a general-purpose processor, a digital signalprocessor (DSP), an application specific or general applicationintegrated circuit (ASIC), a field programmable gate array (FPGA), orother programmable logic devices, discrete gates or transistor logic, ora discrete hardware component, or a combination thereof. Thegeneral-purpose processor may be a microprocessor, or alternatively, theprocessor may be a conventional processor, a controller, amicrocontroller or a state machine. The general-purpose processor oreach circuit described above may be configured by a digital circuit ormay be configured by an analogue circuit. Further, when a technology ofmaking into an integrated circuit superseding integrated circuits at thepresent time appears due to advancement of a semiconductor technology,the integrated circuit by this technology is also able to be used.

Various examples have been described. These and other examples arewithin the scope of the following claims.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119 onprovisional Application No. 62/734,995 on Sep. 21, 2018, No. 62/735,093on Sep. 22, 2018, No. 62/737,049 on Sep. 26, 2018, No. 62/739,263 onSep. 30, 2018, the entire contents of which are hereby incorporated byreference.

1. A method for determining a reference index for a reference picturelist, the method comprising: decoding a reference picture list structurein a sequence parameter set or a slice header; and decoding a referenceindex active override flag in the slice header, in a case that a slicetype is a P slice type or a B slice type, wherein the reference indexactive override flag specifying a number of reference index syntaxelement is present for the P slice and the B slice or a number ofreference index syntax element is present for the B slice.
 2. The methodof claim 2, further comprising: decoding a number of reference indexactive syntax element in the slice header, in a case that a number ofentries in the reference picture list structure is greater than
 1. 3.The method of claim 2, wherein the number of reference index activesyntax element is inferred to be equal to zero, in a case that (i) aslice type of a current slice is the B slice type, (ii) a value of thereference index active override flag is equal to a first value and (iii)the number of reference index active syntax element is not present. 4.The method of claim 2, wherein the number of reference index activesyntax element defined by i equal to zero is inferred to be equal tozero, in a case that (i) a slice type of a current slice is the P slicetype, (ii) a value of the reference index active override flag is equalto a second value, and (iii) the number of reference index active syntaxelement defined by i equal to zero is not present.
 5. A method fordetermining a reference index for a reference picture list, the methodcomprising: encoding a reference picture list structure in a sequenceparameter set or a slice header; and encoding a reference index activeoverride flag in the slice header, in a case that a slice type is a Pslice type or a B slice type, wherein the reference index activeoverride flag specifying a number of reference index syntax element ispresent for the P slice and the B slice or a number of reference indexsyntax element is present for the B slice.
 6. A decoder for decodingdata, the decoder comprising: a processor, and a memory associated withthe processor; wherein the processor is configured to perform thefollowing steps: decoding a reference picture list structure in asequence parameter set or a slice header; and decoding a reference indexactive override flag in the slice header, in a case that a slice type isa P slice type or a B slice type, wherein the reference index activeoverride flag specifying a number of reference index syntax element ispresent for the P slice and the B slice or a number of reference indexsyntax element is present for the B slice.